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| author | Eric S. Raymond <esr@thyrsus.com> | 2002-07-28 09:23:04 +0000 |
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| committer | Eric S. Raymond <esr@thyrsus.com> | 2002-07-28 09:23:04 +0000 |
| commit | 88f8c58d0d2c61effc7a37b10747005ecbf1b381 (patch) | |
| tree | fa7a15336718a14581718e98278164fe7b2bfd5d | |
| parent | fc9faaeb630aca9e1be84f23d234ea4cb17ae660 (diff) | |
| download | fetchmail-88f8c58d0d2c61effc7a37b10747005ecbf1b381.tar.gz fetchmail-88f8c58d0d2c61effc7a37b10747005ecbf1b381.tar.bz2 fetchmail-88f8c58d0d2c61effc7a37b10747005ecbf1b381.zip | |
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diff --git a/design-notes.html b/design-notes.html index bfaff074..d2d48d6b 100644 --- a/design-notes.html +++ b/design-notes.html @@ -1,566 +1,752 @@ -<!doctype HTML PUBLIC "-//W3O//DTD W3 HTML 3.2//EN"> -<HTML> -<HEAD> -<TITLE>Design notes on fetchmail</TITLE> -<link rev=made href="mailto:esr@snark.thyrsus.com"> -<meta name="description" content="Design notes on fetchmail."> -<meta name="keywords" content="fetchmail, POP, POP2, POP3, IMAP, remote mail"> -</HEAD> -<BODY> -<table width="100%" cellpadding=0 summary="Canned page header"><tr> -<td width="30%">Back to <a href="/~esr/index.html">Fetchmail Home Page</a> -<td width="30%" align=center>To <a href="/~esr/sitemap.html">Site Map</a> -<td width="30%" align=right>$Date: 2002/07/28 09:22:19 $ -</tr></table> -<HR> -<H1 ALIGN=CENTER>Design Notes On Fetchmail</H1> - -<p>These notes are for the benefit of future hackers and maintainers. -The following sections are both functional and narrative, read from -beginning to end.</p> - -<H1>History</H1> - -<p>A direct ancestor of the fetchmail program was originally authored -(under the name popclient) by Carl Harris <ceharris@mal.com>. I -took over development in June 1996 and subsequently renamed the -program `fetchmail' to reflect the addition of IMAP support and SMTP -delivery. In early November 1996 Carl officially ended support for -the last popclient versions.</p> - -<p>Before accepting responsibility for the popclient sources from Carl, I -had investigated and used and tinkered with every other UNIX -remote-mail forwarder I could find, including fetchpop1.9, +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml"> +<head> +<title>Design notes on fetchmail</title> +<link rev="made" href="mailto:esr@snark.thyrsus.com" /> +<meta name="description" content="Design notes on fetchmail." /> +<meta name="keywords" content="fetchmail, POP, POP2, POP3, IMAP, remote mail" /> +<style type="text/css"> +/*<![CDATA[*/ + h1.c1 {text-align: center} +/*]]>*/ +</style> +</head> +<body> +<table width="100%" cellpadding="0" summary="Canned page header"> +<tr> +<td width="30%">Back to <a href="/~esr/index.html">Fetchmail Home Page</a></td> +<td width="30%" align="center">To <a href="/~esr/sitemap.html">Site Map</a></td> +<td width="30%" align="right">$Date: 2002/07/28 09:23:04 $</td> +</tr> +</table> + +<hr /> +<h1 class="c1">Design Notes On Fetchmail</h1> + +<p>These notes are for the benefit of future hackers and +maintainers. The following sections are both functional and +narrative, read from beginning to end.</p> + +<h1>History</h1> + +<p>A direct ancestor of the fetchmail program was originally +authored (under the name popclient) by Carl Harris +<ceharris@mal.com>. I took over development in June 1996 and +subsequently renamed the program `fetchmail' to reflect the +addition of IMAP support and SMTP delivery. In early November 1996 +Carl officially ended support for the last popclient versions.</p> + +<p>Before accepting responsibility for the popclient sources from +Carl, I had investigated and used and tinkered with every other +UNIX remote-mail forwarder I could find, including fetchpop1.9, PopTart-0.9.3, get-mail, gwpop, pimp-1.0, pop-perl5-1.2, popc, -popmail-1.6 and upop. My major goal was to get a header-rewrite +popmail-1.6 and upop. My major goal was to get a header-rewrite feature like fetchmail's working so I wouldn't have reply problems anymore.</p> -<p>Despite having done a good bit of work on fetchpop1.9, when I found -popclient I quickly concluded that it offered the solidest base for -future development. I was convinced of this primarily by the presence -of multiple-protocol support. The competition didn't do -POP2/RPOP/APOP, and I was already having vague thoughts of maybe -adding IMAP. (This would advance two other goals: learn IMAP and get -comfortable writing TCP/IP client software.)</p> - -<p>Until popclient 3.05 I was simply following out the implications of -Carl's basic design. He already had daemon.c in the distribution, -and I wanted daemon mode almost as badly as I wanted the header -rewrite feature. The other things I added were bug fixes or -minor extensions.</p> - -<p>After 3.1, when I put in SMTP-forwarding support (more about this -below) the nature of the project changed -- it became a -carefully-thought-out attempt to render obsolete every other program -in its class. The name change quickly followed.</p> - -<H1>The rewrite option</H1> - -<p>MTAs ought to canonicalize the addresses of outgoing non-local mail so -that From:, To:, Cc:, Bcc: and other address headers contain only -fully qualified domain names. Failure to do so can break the reply -function on many mailers. (Sendmail has an option to do this.)</p> +<p>Despite having done a good bit of work on fetchpop1.9, when I +found popclient I quickly concluded that it offered the solidest +base for future development. I was convinced of this primarily by +the presence of multiple-protocol support. The competition didn't +do POP2/RPOP/APOP, and I was already having vague thoughts of maybe +adding IMAP. (This would advance two other goals: learn IMAP and +get comfortable writing TCP/IP client software.)</p> + +<p>Until popclient 3.05 I was simply following out the implications +of Carl's basic design. He already had daemon.c in the +distribution, and I wanted daemon mode almost as badly as I wanted +the header rewrite feature. The other things I added were bug fixes +or minor extensions.</p> + +<p>After 3.1, when I put in SMTP-forwarding support (more about +this below) the nature of the project changed -- it became a +carefully-thought-out attempt to render obsolete every other +program in its class. The name change quickly followed.</p> + +<h1>The rewrite option</h1> + +<p>MTAs ought to canonicalize the addresses of outgoing non-local +mail so that From:, To:, Cc:, Bcc: and other address headers +contain only fully qualified domain names. Failure to do so can +break the reply function on many mailers. (Sendmail has an option +to do this.)</p> <p>This problem only becomes obvious when a reply is generated on a -machine different from where the message was delivered. The -two machines will have different local username spaces, potentially +machine different from where the message was delivered. The two +machines will have different local username spaces, potentially leading to misrouted mail.</p> -<p>Most MTAs (and sendmail in particular) do not canonicalize address headers -in this way (violating RFC 1123). Fetchmail therefore has to do it. This -is the first feature I added to the ancestral popclient.</p> +<p>Most MTAs (and sendmail in particular) do not canonicalize +address headers in this way (violating RFC 1123). Fetchmail +therefore has to do it. This is the first feature I added to the +ancestral popclient.</p> -<H1>Reorganization</H1> +<h1>Reorganization</h1> -<p>The second thing I did reorganize and simplify popclient a lot. Carl -Harris's implementation was very sound, but exhibited a kind of -unnecessary complexity common to many C programmers. He treated the -code as central and the data structures as support for the code. As a -result, the code was beautiful but the data structure design ad-hoc -and rather ugly (at least to this old LISP hacker).</p> +<p>The second thing I did reorganize and simplify popclient a lot. +Carl Harris's implementation was very sound, but exhibited a kind +of unnecessary complexity common to many C programmers. He treated +the code as central and the data structures as support for the +code. As a result, the code was beautiful but the data structure +design ad-hoc and rather ugly (at least to this old LISP +hacker).</p> -<p>I was able to improve matters significantly by reorganizing most of the -program around the `query' data structure and eliminating a bunch of -global context. This especially simplified the main sequence in -fetchmail.c and was critical in enabling the daemon mode changes.</p> +<p>I was able to improve matters significantly by reorganizing most +of the program around the `query' data structure and eliminating a +bunch of global context. This especially simplified the main +sequence in fetchmail.c and was critical in enabling the daemon +mode changes.</p> -<H1>IMAP support and the method table</H1> +<h1>IMAP support and the method table</h1> -<p>The next step was IMAP support. I initially wrote the IMAP code -as a generic query driver and a method table. The idea was to have +<p>The next step was IMAP support. I initially wrote the IMAP code +as a generic query driver and a method table. The idea was to have all the protocol-independent setup logic and flow of control in the driver, and the protocol-specific stuff in the method table.</p> -<p>Once this worked, I rewrote the POP3 code to use the same organization. -The POP2 code kept its own driver for a couple more releases, until -I found sources of a POP2 server to test against (the breed seems -to be nearly extinct).</p> - -<p>The purpose of this reorganization, of course, is to trivialize -the development of support for future protocols as much as possible. -All mail-retrieval protocols have to have pretty similar logical -design by the nature of the task. By abstracting out that common -logic and its interface to the rest of the program, both the common -and protocol-specific parts become easier to understand.</p> - -<p>Furthermore, many kinds of new features can instantly be supported -across all protocols by modifying the one driver module.</p> - -<H1>Implications of smtp forwarding</H1> - -<p>The direction of the project changed radically when Harry Hochheiser -sent me his scratch code for forwarding fetched mail to the SMTP port. -I realized almost immediately that a reliable implementation of this -feature would make all the other delivery modes obsolete.</p> - -<p>Why mess with all the complexity of configuring an MDA or setting up -lock-and-append on a mailbox when port 25 is guaranteed to be there on -any platform with TCP/IP support in the first place? Especially when -this means retrieved mail is guaranteed to look like normal sender- -initiated SMTP mail, which is really what we want anyway.</p> - -<p>Clearly, the right thing to do was (1) hack SMTP forwarding support -into the generic driver, (2) make it the default mode, and (3) eventually -throw out all the other delivery modes. </p> - -<p>I hesitated over step 3 for some time, fearing to upset long-time -popclient users dependent on the alternate delivery mechanisms. In -theory, they could immediately switch to .forward files or their -non-sendmail equivalents to get the same effects. In practice the -transition might have been messy.</p> - -<p>But when I did it (see the NEWS note on the great options massacre) -the benefits proved huge. The cruftiest parts of the driver code -vanished. Configuration got radically simpler -- no more grovelling -around for the system MDA and user's mailbox, no more worries about -whether the underlying OS supports file locking.</p> - -<p>Also, the only way to lose mail vanished. If you specified localfolder -and the disk got full, your mail got lost. This can't happen with -SMTP forwarding because your SMTP listener won't return OK unless -the message can be spooled or processed.</p> - -<p>Also, performance improved (though not so you'd notice it in a single -run). Another not insignificant benefit of this change was that the -manual page got a lot simpler.</p> - -<p>Later, I had to bring --mda back in order to allow handling of some -obscure situations involving dynamic SLIP. But I found a much simpler -way to do it.</p> - -<p>The moral? Don't hesitate to throw away superannuated features when -you can do it without loss of effectiveness. I tanked a couple I'd -added myself and have no regrets at all. As Saint-Exupery said, -"Perfection [in design] is achieved not when there is nothing more to -add, but rather when there is nothing more to take away." This +<p>Once this worked, I rewrote the POP3 code to use the same +organization. The POP2 code kept its own driver for a couple more +releases, until I found sources of a POP2 server to test against +(the breed seems to be nearly extinct).</p> + +<p>The purpose of this reorganization, of course, is to trivialize +the development of support for future protocols as much as +possible. All mail-retrieval protocols have to have pretty similar +logical design by the nature of the task. By abstracting out that +common logic and its interface to the rest of the program, both the +common and protocol-specific parts become easier to understand.</p> + +<p>Furthermore, many kinds of new features can instantly be +supported across all protocols by modifying the one driver +module.</p> + +<h1>Implications of smtp forwarding</h1> + +<p>The direction of the project changed radically when Harry +Hochheiser sent me his scratch code for forwarding fetched mail to +the SMTP port. I realized almost immediately that a reliable +implementation of this feature would make all the other delivery +modes obsolete.</p> + +<p>Why mess with all the complexity of configuring an MDA or +setting up lock-and-append on a mailbox when port 25 is guaranteed +to be there on any platform with TCP/IP support in the first place? +Especially when this means retrieved mail is guaranteed to look +like normal sender- initiated SMTP mail, which is really what we +want anyway.</p> + +<p>Clearly, the right thing to do was (1) hack SMTP forwarding +support into the generic driver, (2) make it the default mode, and +(3) eventually throw out all the other delivery modes.</p> + +<p>I hesitated over step 3 for some time, fearing to upset +long-time popclient users dependent on the alternate delivery +mechanisms. In theory, they could immediately switch to .forward +files or their non-sendmail equivalents to get the same effects. In +practice the transition might have been messy.</p> + +<p>But when I did it (see the NEWS note on the great options +massacre) the benefits proved huge. The cruftiest parts of the +driver code vanished. Configuration got radically simpler -- no +more grovelling around for the system MDA and user's mailbox, no +more worries about whether the underlying OS supports file +locking.</p> + +<p>Also, the only way to lose mail vanished. If you specified +localfolder and the disk got full, your mail got lost. This can't +happen with SMTP forwarding because your SMTP listener won't return +OK unless the message can be spooled or processed.</p> + +<p>Also, performance improved (though not so you'd notice it in a +single run). Another not insignificant benefit of this change was +that the manual page got a lot simpler.</p> + +<p>Later, I had to bring --mda back in order to allow handling of +some obscure situations involving dynamic SLIP. But I found a much +simpler way to do it.</p> + +<p>The moral? Don't hesitate to throw away superannuated features +when you can do it without loss of effectiveness. I tanked a couple +I'd added myself and have no regrets at all. As Saint-Exupery said, +"Perfection [in design] is achieved not when there is nothing more +to add, but rather when there is nothing more to take away." This program isn't perfect, but it's trying.</p> -<H1>The most-requested features that I will never add, and why not:</H1> +<h1>The most-requested features that I will never add, and why +not:</h1> -<H2>Password encryption in .fetchmailrc</H2> +<h2>Password encryption in .fetchmailrc</h2> -<p>The reason there's no facility to store passwords encrypted in the -.fetchmailrc file is because this doesn't actually add protection.</p> +<p>The reason there's no facility to store passwords encrypted in +the .fetchmailrc file is because this doesn't actually add +protection.</p> <p>Anyone who's acquired the 0600 permissions needed to read your -.fetchmailrc file will be able to run fetchmail as you anyway -- and -if it's your password they're after, they'd be able to rip the +.fetchmailrc file will be able to run fetchmail as you anyway -- +and if it's your password they're after, they'd be able to rip the necessary decoder out of the fetchmail code itself to get it.</p> <p>All .fetchmailrc encryption would do is give a false sense of security to people who don't think very hard.</p> -<H2>Truly concurrent queries to multiple hosts</H2> +<h2>Truly concurrent queries to multiple hosts</h2> -<p>Occasionally I get a request for this on "efficiency" grounds. These -people aren't thinking either. True concurrency would do nothing to lessen -fetchmail's total IP volume. The best it could possibly do is change the -usage profile to shorten the duration of the active part of a poll cycle -at the cost of increasing its demand on IP volume per unit time.</p> +<p>Occasionally I get a request for this on "efficiency" grounds. +These people aren't thinking either. True concurrency would do +nothing to lessen fetchmail's total IP volume. The best it could +possibly do is change the usage profile to shorten the duration of +the active part of a poll cycle at the cost of increasing its +demand on IP volume per unit time.</p> -<p>If one could thread the protocol code so that fetchmail didn't block -on waiting for a protocol response, but rather switched to trying to -process another host query, one might get an efficiency gain (close to -constant loading at the single-host level).</p> +<p>If one could thread the protocol code so that fetchmail didn't +block on waiting for a protocol response, but rather switched to +trying to process another host query, one might get an efficiency +gain (close to constant loading at the single-host level).</p> -<p>Fortunately, I've only seldom seen a server that incurred significant -wait time on an individual response. I judge the gain from this not -worth the hideous complexity increase it would require in the code.</p> +<p>Fortunately, I've only seldom seen a server that incurred +significant wait time on an individual response. I judge the gain +from this not worth the hideous complexity increase it would +require in the code.</p> -<H2>Multiple concurrent instances of fetchmail</H2> +<h2>Multiple concurrent instances of fetchmail</h2> -<p>Fetchmail locking is on a per-invoking-user because finer-grained -locks would be really hard to implement in a portable way. The -problem is that you don't want two fetchmails querying the same site -for the same remote user at the same time.</p> +<p>Fetchmail locking is on a per-invoking-user because +finer-grained locks would be really hard to implement in a portable +way. The problem is that you don't want two fetchmails querying the +same site for the same remote user at the same time.</p> -<p>To handle this optimally, multiple fetchmails would have to associate -a system-wide semaphore with each active pair of a remote user and -host canonical address. A fetchmail would have to block until getting -this semaphore at the start of a query, and release it at the end of a -query.</p> +<p>To handle this optimally, multiple fetchmails would have to +associate a system-wide semaphore with each active pair of a remote +user and host canonical address. A fetchmail would have to block +until getting this semaphore at the start of a query, and release +it at the end of a query.</p> -<p>This would be way too complicated to do just for an "it might be nice" -feature. Instead, you can run a single root fetchmail polling for -multiple users in either single-drop or multidrop mode.</p> +<p>This would be way too complicated to do just for an "it might be +nice" feature. Instead, you can run a single root fetchmail polling +for multiple users in either single-drop or multidrop mode.</p> -<p>The fundamental problem here is how an instance of fetchmail polling -host foo can assert that it's doing so in a way visible to all other -fetchmails. System V semaphores would be ideal for this purpose, but -they're not portable.</p> +<p>The fundamental problem here is how an instance of fetchmail +polling host foo can assert that it's doing so in a way visible to +all other fetchmails. System V semaphores would be ideal for this +purpose, but they're not portable.</p> -<p>I've thought about this a lot and roughed up several designs. All are -complicated and fragile, with a bunch of the standard problems (what -happens if a fetchmail aborts before clearing its semaphore, and how -do we recover reliably?).</p> +<p>I've thought about this a lot and roughed up several designs. +All are complicated and fragile, with a bunch of the standard +problems (what happens if a fetchmail aborts before clearing its +semaphore, and how do we recover reliably?).</p> -<p>I'm just not satisfied that there's enough functional gain here to pay -for the large increase in complexity that adding these semaphores -would entail.</p> +<p>I'm just not satisfied that there's enough functional gain here +to pay for the large increase in complexity that adding these +semaphores would entail.</p> -<H1>Multidrop and alias handling</H1> +<h1>Multidrop and alias handling</h1> -<p>I decided to add the multidrop support partly because some users were -clamoring for it, but mostly because I thought it would shake bugs out -of the single-drop code by forcing me to deal with addressing in full -generality. And so it proved.</p> +<p>I decided to add the multidrop support partly because some users +were clamoring for it, but mostly because I thought it would shake +bugs out of the single-drop code by forcing me to deal with +addressing in full generality. And so it proved.</p> <p>There are two important aspects of the features for handling -multiple-drop aliases and mailing lists which future hackers should be -careful to preserve.</p> - -<OL> -<LI> - <p>The logic path for single-recipient mailboxes doesn't involve header - parsing or DNS lookups at all. This is important -- it means the code - for the most common case can be much simpler and more robust.</p> - -<LI> - <p>The multidrop handing does <EM>not</EM> rely on doing the equivalent of - passing the message to sendmail -oem -t. Instead, it explicitly mines - members of a specified set of local usernames out of the header.</p> - -<LI> - <p>We do <EM>not</EM> attempt delivery to multidrop mailboxes in the presence - of DNS errors. Before each multidrop poll we probe DNS to see if we have a - nameserver handy. If not, the poll is skipped. If DNS crashes during a - poll, the error return from the next nameserver lookup aborts message - delivery and ends the poll. The daemon mode will then quietly spin until - DNS comes up again, at which point it will resume delivering mail.</p> -</OL> - -<p>When I designed this support, I was terrified of doing anything that could -conceivably cause a mail loop (you should be too). That's why the code -as written can only append <EM>local</EM> names (never @-addresses) to the -recipients list.</p> - -<p>The code in mxget.c is nasty, no two ways about it. But it's utterly -necessary, there are a lot of MX pointers out there. It really ought -to be a (documented!) entry point in the bind library.</p> - -<H1>DNS error handling</H1> +multiple-drop aliases and mailing lists which future hackers should +be careful to preserve.</p> + +<ol> +<li> +<p>The logic path for single-recipient mailboxes doesn't involve +header parsing or DNS lookups at all. This is important -- it means +the code for the most common case can be much simpler and more +robust.</p> +</li> + +<li> +<p>The multidrop handing does <em>not</em> rely on doing the +equivalent of passing the message to sendmail -oem -t. Instead, it +explicitly mines members of a specified set of local usernames out +of the header.</p> +</li> + +<li> +<p>We do <em>not</em> attempt delivery to multidrop mailboxes in +the presence of DNS errors. Before each multidrop poll we probe DNS +to see if we have a nameserver handy. If not, the poll is skipped. +If DNS crashes during a poll, the error return from the next +nameserver lookup aborts message delivery and ends the poll. The +daemon mode will then quietly spin until DNS comes up again, at +which point it will resume delivering mail.</p> +</li> +</ol> + +<p>When I designed this support, I was terrified of doing anything +that could conceivably cause a mail loop (you should be too). +That's why the code as written can only append <em>local</em> names +(never @-addresses) to the recipients list.</p> + +<p>The code in mxget.c is nasty, no two ways about it. But it's +utterly necessary, there are a lot of MX pointers out there. It +really ought to be a (documented!) entry point in the bind +library.</p> + +<h1>DNS error handling</h1> <p>Fetchmail's behavior on DNS errors is to suppress forwarding and deletion of the individual message that each occurs in, leaving it -queued on the server for retrieval on a subsequent poll. The -assumption is that DNS errors are transient, due to temporary server -outages.</p> - -<p>Unfortunately this means that if a DNS error is permanent a message -can be perpetually stuck in the server mailbox. We've had a couple -bug reports of this kind due to subtle RFC822 parsing errors in the fetchmail -code that resulted in impossible things getting passed to the DNS lookup -routines.</p> - -<p>Alternative ways to handle the problem: ignore DNS errors (treating -them as a non-match on the mailserver domain), or forward messages -with errors to fetchmail's invoking user in addition to any other -recipients. These would fit an assumption that DNS lookup errors are -likely to be permanent problems associated with an address.</p> - -<H1>IPv6 and IPSEC</H1> - -<p>The IPv6 support patches are really more protocol-family independence -patches. Because of this, in most places, "ports" (numbers) have been -replaced with "services" (strings, that may be digits). This allows us -to run with certain protocols that use strings as "service names" -where we in the IP world think of port numbers. Someday we'll plumb -strings all over and then, if inet6 is not enabled, do a -getservbyname() down in SocketOpen. The IPv6 support patches use -getaddrinfo(), which is a POSIX p1003.1g mandated function. So, in the -not too distant future, we'll zap the ifdefs and just let autoconf -check for getaddrinfo. IPv6 support comes pretty much automatically -once you have protocol family independence.</p> - -<H1>Internationalization</H1> +queued on the server for retrieval on a subsequent poll. The +assumption is that DNS errors are transient, due to temporary +server outages.</p> + +<p>Unfortunately this means that if a DNS error is permanent a +message can be perpetually stuck in the server mailbox. We've had a +couple bug reports of this kind due to subtle RFC822 parsing errors +in the fetchmail code that resulted in impossible things getting +passed to the DNS lookup routines.</p> + +<p>Alternative ways to handle the problem: ignore DNS errors +(treating them as a non-match on the mailserver domain), or forward +messages with errors to fetchmail's invoking user in addition to +any other recipients. These would fit an assumption that DNS lookup +errors are likely to be permanent problems associated with an +address.</p> + +<h1>IPv6 and IPSEC</h1> + +<p>The IPv6 support patches are really more protocol-family +independence patches. Because of this, in most places, "ports" +(numbers) have been replaced with "services" (strings, that may be +digits). This allows us to run with certain protocols that use +strings as "service names" where we in the IP world think of port +numbers. Someday we'll plumb strings all over and then, if inet6 is +not enabled, do a getservbyname() down in SocketOpen. The IPv6 +support patches use getaddrinfo(), which is a POSIX p1003.1g +mandated function. So, in the not too distant future, we'll zap the +ifdefs and just let autoconf check for getaddrinfo. IPv6 support +comes pretty much automatically once you have protocol family +independence.</p> + +<h1>Internationalization</h1> <p>Internationalization is handled using GNU gettext (see the file -ABOUT_NLS in the source distribution). This places some -minor constraints on the code.</p> +ABOUT_NLS in the source distribution). This places some minor +constraints on the code.</p> -<p>Strings that must be subject to translation should be wrapped with GT_() -or N_() -- the former in function arguments, the latter in static -initializers and other non-function-argument contexts.</p> +<p>Strings that must be subject to translation should be wrapped +with GT_() or N_() -- the former in function arguments, the latter +in static initializers and other non-function-argument +contexts.</p> -<H1>Checklist for Adding Options</H1> +<h1>Checklist for Adding Options</h1> -<p>Adding a control option is not complicated in principle, but there are -a lot of fiddly details in the process. You'll need to do the -following minimum steps.</p> +<p>Adding a control option is not complicated in principle, but +there are a lot of fiddly details in the process. You'll need to do +the following minimum steps.</p> -<UL> -<LI>Add a field to represent the control in <code>struct run</code>, - <code>struct query</code>, or <code>struct hostdata</code>. +<ul> +<li>Add a field to represent the control in <code>struct +run</code>, <code>struct query</code>, or <code>struct +hostdata</code>.</li> -<LI>Go to <code>rcfile_y.y</code>. Add the token to the grammar. Don't - forget the <code>%token</code> declaration. +<li>Go to <code>rcfile_y.y</code>. Add the token to the grammar. +Don't forget the <code>%token</code> declaration.</li> -<LI>Pick an actual string to declare the option in the .fetchmailrc file. Add - the token to <code>rcfile_l</code>. +<li>Pick an actual string to declare the option in the .fetchmailrc +file. Add the token to <code>rcfile_l</code>.</li> -<LI>Pick a long-form option name, and a one-letter short option if any - are left. Go to <code>options.c</code>. Pick a new <code>LA_</code> - value. Hack the <code>longoptions</code> table to set up the - association. Hack the big switch statement to set the option. - Hack the `?' message to describe it. +<li>Pick a long-form option name, and a one-letter short option if +any are left. Go to <code>options.c</code>. Pick a new +<code>LA_</code> value. Hack the <code>longoptions</code> table to +set up the association. Hack the big switch statement to set the +option. Hack the `?' message to describe it.</li> -<LI>If the default is nonzero, set it in <code>def_opts</code> near the top of - <code>load_params</code> in <code>fetchmail.c</code>. +<li>If the default is nonzero, set it in <code>def_opts</code> near +the top of <code>load_params</code> in +<code>fetchmail.c</code>.</li> -<LI>Add code to dump the option value in <code>fetchmail.c:dump_params</code>. +<li>Add code to dump the option value in +<code>fetchmail.c:dump_params</code>.</li> -<LI> For a per-site or per-user option, add proper - <code>FLAG_MERGE</code> actions in fetchmail.c's optmerge() - function. For a global option, add an override at the end of - load_params; this will involve copying a "cmd_run." field to a - corresponding "run." field, see the existing code for models. +<li>For a per-site or per-user option, add proper +<code>FLAG_MERGE</code> actions in fetchmail.c's optmerge() +function. For a global option, add an override at the end of +load_params; this will involve copying a "cmd_run." field to a +corresponding "run." field, see the existing code for models.</li> -<LI>Document the option in fetchmail.man. This will require at least - two changes; one to the collected table of options, and one full - text description of the option. +<li>Document the option in fetchmail.man. This will require at +least two changes; one to the collected table of options, and one +full text description of the option.</li> -<LI>Hack fetchmailconf to configure it. Bump the fetchmailconf version. +<li>Hack fetchmailconf to configure it. Bump the fetchmailconf +version.</li> -<LI>Hack conf.c to dump the option so we won't have a version-skew problem. +<li>Hack conf.c to dump the option so we won't have a version-skew +problem.</li> -<LI>Add an entry to NEWS. +<li>Add an entry to NEWS.</li> -<LI>If the option implements a new feature, add a note to the feature list. -</UL> +<li>If the option implements a new feature, add a note to the +feature list.</li> +</ul> -<p>There may be other things you have to do in the way of logic, of course.</p> +<p>There may be other things you have to do in the way of logic, of +course.</p> -<p>Before you implement an option, though, think hard. Is there any way -to make fetchmail automatically detect the circumstances under which -it should change its behavior? If so, don't write an option. Just do -the check!</p> +<p>Before you implement an option, though, think hard. Is there any +way to make fetchmail automatically detect the circumstances under +which it should change its behavior? If so, don't write an option. +Just do the check!</p> -<H1>Lessons learned</H1> +<h1>Lessons learned</h1> -<H3>1. Server-side state is essential</H3> +<h3>1. Server-side state is essential</h3> -<p>The person(s) responsible for removing LAST from POP3 deserve to suffer. -Without it, a client has no way to know which messages in a box have been -read by other means, such as an MUA running on the server.</p> +<p>The person(s) responsible for removing LAST from POP3 deserve to +suffer. Without it, a client has no way to know which messages in a +box have been read by other means, such as an MUA running on the +server.</p> <p>The POP3 UID feature described in RFC1725 to replace LAST is -insufficient. The only problem it solves is tracking which messages -have been read <EM>by this client</EM> -- and even that requires +insufficient. The only problem it solves is tracking which messages +have been read <em>by this client</em> -- and even that requires tricky, fragile implementation.</p> <p>The underlying lesson is that maintaining accessible server-side -`seen' state bits associated with Status headers is indispensible in a -Unix/RFC822 mail server protocol. IMAP gets this right.</p> +`seen' state bits associated with Status headers is indispensible +in a Unix/RFC822 mail server protocol. IMAP gets this right.</p> -<H3>2. Readable text protocol transactions are a Good Thing</H3> +<h3>2. Readable text protocol transactions are a Good Thing</h3> -<p>A nice thing about the general class of text-based protocols that SMTP, -POP2, POP3, and IMAP belongs to is that client/server transactions are -easy to watch and transaction code correspondingly easy to debug. Given -a decent layer of socket utility functions (which Carl provided) it's -easy to write protocol engines and not hard to show that they're working -correctly.</p> +<p>A nice thing about the general class of text-based protocols +that SMTP, POP2, POP3, and IMAP belongs to is that client/server +transactions are easy to watch and transaction code correspondingly +easy to debug. Given a decent layer of socket utility functions +(which Carl provided) it's easy to write protocol engines and not +hard to show that they're working correctly.</p> -<p>This is an advantage not to be despised! Because of it, this project has -been interesting and fun -- no serious or persistent bugs, no long -hours spent looking for subtle pathologies.</p> +<p>This is an advantage not to be despised! Because of it, this +project has been interesting and fun -- no serious or persistent +bugs, no long hours spent looking for subtle pathologies.</p> -<H3>3. IMAP is a Good Thing.</H3> +<h3>3. IMAP is a Good Thing.</h3> -<p>Now that there is a standard IMAP equivalent of the POP3 APOP validation -in CRAM-MD5, POP3 is completely obsolete.</p> +<p>Now that there is a standard IMAP equivalent of the POP3 APOP +validation in CRAM-MD5, POP3 is completely obsolete.</p> -<H3>4. SMTP is the Right Thing</H3> +<h3>4. SMTP is the Right Thing</h3> -<p>In retrospect it seems clear that this program (and others like it) -should have been designed to forward via SMTP from the beginning. -This lesson may be applicable to other Unix programs that now call the -local MDA/MTA as a program.</p> +<p>In retrospect it seems clear that this program (and others like +it) should have been designed to forward via SMTP from the +beginning. This lesson may be applicable to other Unix programs +that now call the local MDA/MTA as a program.</p> -<H3>5. Syntactic noise can be your friend</H3> +<h3>5. Syntactic noise can be your friend</h3> -<p>The optional `noise' keywords in the rc file syntax started out as -a late-night experiment. The English-like syntax they allow is +<p>The optional `noise' keywords in the rc file syntax started out +as a late-night experiment. The English-like syntax they allow is considerably more readable than the traditional terse keyword-value -pairs you get when you strip them all out. I think there may be a +pairs you get when you strip them all out. I think there may be a wider lesson here.</p> -<H1>Motivation and validation</H1> +<h1>Motivation and validation</h1> -<p>It is truly written: the best hacks start out as personal solutions to -the author's everyday problems, and spread because the problem turns -out to be typical for a large class of users. So it was with Carl Harris -and the ancestral popclient, and so with me and fetchmail.</p> +<p>It is truly written: the best hacks start out as personal +solutions to the author's everyday problems, and spread because the +problem turns out to be typical for a large class of users. So it +was with Carl Harris and the ancestral popclient, and so with me +and fetchmail.</p> -<p>It's gratifying that fetchmail has become so popular. Until just before -1.9 I was designing strictly to my own taste. The multi-drop mailbox -support and the new --limit option were the first features to go in that -I didn't need myself.</p> +<p>It's gratifying that fetchmail has become so popular. Until just +before 1.9 I was designing strictly to my own taste. The multi-drop +mailbox support and the new --limit option were the first features +to go in that I didn't need myself.</p> -<p>By 1.9, four months after I started hacking on popclient and a month -after the first fetchmail release, there were literally a hundred -people on the fetchmail-friends contact list. That's pretty powerful -motivation. And they were a good crowd, too, sending fixes and -intelligent bug reports in volume. A user population like that is -a gift from the gods, and this is my expression of gratitude.</p> +<p>By 1.9, four months after I started hacking on popclient and a +month after the first fetchmail release, there were literally a +hundred people on the fetchmail-friends contact list. That's pretty +powerful motivation. And they were a good crowd, too, sending fixes +and intelligent bug reports in volume. A user population like that +is a gift from the gods, and this is my expression of +gratitude.</p> -<p>The beta testers didn't know it at the time, but they were also the -subjects of a sociological experiment. The results are described in -my paper, <A -HREF="//www.tuxedo.org/~esr/writings/cathedral-bazaar/">The Cathedral -And The Bazaar</A>.</p> +<p>The beta testers didn't know it at the time, but they were also +the subjects of a sociological experiment. The results are +described in my paper, <a +href="//www.tuxedo.org/~esr/writings/cathedral-bazaar/">The +Cathedral And The Bazaar</a>.</p> -<H1>Credits</H1> +<h1>Credits</h1> -<p>Special thanks go to Carl Harris, who built a good solid code base -and then tolerated me hacking it out of recognition. And to Harry -Hochheiser, who gave me the idea of the SMTP-forwarding delivery mode.</p> +<p>Special thanks go to Carl Harris, who built a good solid code +base and then tolerated me hacking it out of recognition. And to +Harry Hochheiser, who gave me the idea of the SMTP-forwarding +delivery mode.</p> -<p>Other significant contributors to the code have included Dave Bodenstab -(error.c code and --syslog), George Sipe (--monitor and --interface), -Gordon Matzigkeit (netrc.c), Al Longyear (UIDL support), Chris -Hanson (Kerberos V4 support), and Craig Metz (OPIE, IPv6, IPSEC).</p> +<p>Other significant contributors to the code have included Dave +Bodenstab (error.c code and --syslog), George Sipe (--monitor and +--interface), Gordon Matzigkeit (netrc.c), Al Longyear (UIDL +support), Chris Hanson (Kerberos V4 support), and Craig Metz (OPIE, +IPv6, IPSEC).</p> -<H1>Conclusion</H1> +<h1>Conclusion</h1> <p>At this point, the fetchmail code appears to be pretty stable. -It will probably undergo substantial change only if and when support -for a new retrieval protocol or authentication method is added.</p> - -<H1>Relevant RFCS</H1> - -<p>Not all of these describe standards explicitly used in fetchmail, but they -all shaped the design in one way or another.</p> - -<DL> -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc821.txt">RFC821</A> -<DD> SMTP protocol -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc822.txt">RFC822</A> -<DD> Mail header format -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc937.txt">RFC937</A> -<DD> Post Office Protocol - Version 2 -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc974.txt">RFC974</A> -<DD> MX routing -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc976.txt">RFC976</A> -<DD> UUCP mail format -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1081.txt">RFC1081</A> -<DD> Post Office Protocol - Version 3 -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1123.txt">RFC1123</A> -<DD> Host requirements (modifies 821, 822, and 974) -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1176.txt">RFC1176</A> -<DD> Interactive Mail Access Protocol - Version 2 -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1203.txt">RFC1203</A> -<DD> Interactive Mail Access Protocol - Version 3 -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1225.txt">RFC1225</A> -<DD> Post Office Protocol - Version 3 -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1344.txt">RFC1344</A> -<DD> Implications of MIME for Internet Mail Gateways -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1413.txt">RFC1413</A> -<DD> Identification server -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1428.txt">RFC1428</A> -<DD> Transition of Internet Mail from Just-Send-8 to 8-bit SMTP/MIME -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1460.txt">RFC1460</A> -<DD> Post Office Protocol - Version 3 -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1508.txt">RFC1508</A> -<DD> Generic Security Service Application Program Interface -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1521.txt">RFC1521</A> -<DD> MIME: Multipurpose Internet Mail Extensions -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1869.txt">RFC1869</A> -<DD> SMTP Service Extensions (ESMTP spec) -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1652.txt">RFC1652</A> -<DD> SMTP Service Extension for 8bit-MIMEtransport -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1725.txt">RFC1725</A> -<DD> Post Office Protocol - Version 3 -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1730.txt">RFC1730</A> -<DD> Interactive Mail Access Protocol - Version 4 -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1731.txt">RFC1731</A> -<DD> IMAP4 Authentication Mechanisms -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1732.txt">RFC1732</A> -<DD> IMAP4 Compatibility With IMAP2 And IMAP2bis -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1734.txt">RFC1734</A> -<DD> POP3 AUTHentication command -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1870.txt">RFC1870</A> -<DD> SMTP Service Extension for Message Size Declaration -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1891.txt">RFC1891</A> -<DD> SMTP Service Extension for Delivery Status Notifications -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1892.txt">RFC1892</A> -<DD> The Multipart/Report Content Type for the Reporting of Mail System Administrative Messages -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1894.txt">RFC1894</A> -<DD>An Extensible Message Format for Delivery Status Notifications -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1893.txt">RFC1893</A> -<DD> Enhanced Mail System Status Codes -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1894.txt">RFC1894</A> -<DD> An Extensible Message Format for Delivery Status Notifications -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1938.txt">RFC1938</A> -<DD> A One-Time Password System -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1939.txt">RFC1939</A> -<DD> Post Office Protocol - Version 3 -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1957.txt">RFC1957</A> -<DD> Some Observations on Implementations of the Post Office Protocol (POP3) -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc1985.txt">RFC1985</A> -<DD> SMTP Service Extension for Remote Message Queue Starting -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc2033.txt">RFC2033</A> -<DD> Local Mail Transfer Protocol -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc2060.txt">RFC2060</A> -<DD> Internet Message Access Protocol - Version 4rev1 -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc2061.txt">RFC2061</A> -<DD> IMAP4 Compatibility With IMAP2bis -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc2062.txt">RFC2062</A> -<DD> Internet Message Access Protocol - Obsolete Syntax -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc2195.txt">RFC2195</A> -<DD> IMAP/POP AUTHorize Extension for Simple Challenge/Response -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc2177.txt">RFC2177</A> -<DD> IMAP IDLE command -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc2449.txt">RFC2449</A> -<DD> POP3 Extension Mechanism -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc2554.txt">RFC2554</A> -<DD> SMTP Service Extension for Authentication -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc2595.txt">RFC2595</A> -<DD> Using TLS with IMAP, POP3 and ACAP -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc2645.txt">RFC2645</A> -<DD>On-Demand Mail Relay: SMTP with Dynamic IP Addresses -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc2683.txt">RFC2683</A> -<DD> IMAP4 Implementation Recommendations -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc2821.txt">RFC2821</A> -<DD> Simple Mail Transfer Protocol -<DT><A HREF="ftp://ftp.isi.edu/in-notes/rfc2822.txt">RFC2822</A> -<DD>Internet Message Format -</DL> +It will probably undergo substantial change only if and when +support for a new retrieval protocol or authentication method is +added.</p> + +<h1>Relevant RFCS</h1> + +<p>Not all of these describe standards explicitly used in +fetchmail, but they all shaped the design in one way or +another.</p> + +<dl> +<dt><a href="ftp://ftp.isi.edu/in-notes/rfc821.txt">RFC821</a></dt> + +<dd>SMTP protocol</dd> + +<dt><a href="ftp://ftp.isi.edu/in-notes/rfc822.txt">RFC822</a></dt> + +<dd>Mail header format</dd> + +<dt><a href="ftp://ftp.isi.edu/in-notes/rfc937.txt">RFC937</a></dt> + +<dd>Post Office Protocol - Version 2</dd> + +<dt><a href="ftp://ftp.isi.edu/in-notes/rfc974.txt">RFC974</a></dt> + +<dd>MX routing</dd> + +<dt><a href="ftp://ftp.isi.edu/in-notes/rfc976.txt">RFC976</a></dt> + +<dd>UUCP mail format</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1081.txt">RFC1081</a></dt> + +<dd>Post Office Protocol - Version 3</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1123.txt">RFC1123</a></dt> + +<dd>Host requirements (modifies 821, 822, and 974)</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1176.txt">RFC1176</a></dt> + +<dd>Interactive Mail Access Protocol - Version 2</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1203.txt">RFC1203</a></dt> + +<dd>Interactive Mail Access Protocol - Version 3</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1225.txt">RFC1225</a></dt> + +<dd>Post Office Protocol - Version 3</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1344.txt">RFC1344</a></dt> + +<dd>Implications of MIME for Internet Mail Gateways</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1413.txt">RFC1413</a></dt> + +<dd>Identification server</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1428.txt">RFC1428</a></dt> + +<dd>Transition of Internet Mail from Just-Send-8 to 8-bit +SMTP/MIME</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1460.txt">RFC1460</a></dt> + +<dd>Post Office Protocol - Version 3</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1508.txt">RFC1508</a></dt> + +<dd>Generic Security Service Application Program Interface</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1521.txt">RFC1521</a></dt> + +<dd>MIME: Multipurpose Internet Mail Extensions</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1869.txt">RFC1869</a></dt> + +<dd>SMTP Service Extensions (ESMTP spec)</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1652.txt">RFC1652</a></dt> + +<dd>SMTP Service Extension for 8bit-MIMEtransport</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1725.txt">RFC1725</a></dt> + +<dd>Post Office Protocol - Version 3</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1730.txt">RFC1730</a></dt> + +<dd>Interactive Mail Access Protocol - Version 4</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1731.txt">RFC1731</a></dt> + +<dd>IMAP4 Authentication Mechanisms</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1732.txt">RFC1732</a></dt> + +<dd>IMAP4 Compatibility With IMAP2 And IMAP2bis</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1734.txt">RFC1734</a></dt> + +<dd>POP3 AUTHentication command</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1870.txt">RFC1870</a></dt> + +<dd>SMTP Service Extension for Message Size Declaration</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1891.txt">RFC1891</a></dt> + +<dd>SMTP Service Extension for Delivery Status Notifications</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1892.txt">RFC1892</a></dt> + +<dd>The Multipart/Report Content Type for the Reporting of Mail +System Administrative Messages</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1894.txt">RFC1894</a></dt> + +<dd>An Extensible Message Format for Delivery Status +Notifications</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1893.txt">RFC1893</a></dt> + +<dd>Enhanced Mail System Status Codes</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1894.txt">RFC1894</a></dt> + +<dd>An Extensible Message Format for Delivery Status +Notifications</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1938.txt">RFC1938</a></dt> + +<dd>A One-Time Password System</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1939.txt">RFC1939</a></dt> + +<dd>Post Office Protocol - Version 3</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1957.txt">RFC1957</a></dt> + +<dd>Some Observations on Implementations of the Post Office +Protocol (POP3)</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc1985.txt">RFC1985</a></dt> + +<dd>SMTP Service Extension for Remote Message Queue Starting</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc2033.txt">RFC2033</a></dt> + +<dd>Local Mail Transfer Protocol</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc2060.txt">RFC2060</a></dt> + +<dd>Internet Message Access Protocol - Version 4rev1</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc2061.txt">RFC2061</a></dt> + +<dd>IMAP4 Compatibility With IMAP2bis</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc2062.txt">RFC2062</a></dt> + +<dd>Internet Message Access Protocol - Obsolete Syntax</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc2195.txt">RFC2195</a></dt> + +<dd>IMAP/POP AUTHorize Extension for Simple Challenge/Response</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc2177.txt">RFC2177</a></dt> + +<dd>IMAP IDLE command</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc2449.txt">RFC2449</a></dt> + +<dd>POP3 Extension Mechanism</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc2554.txt">RFC2554</a></dt> + +<dd>SMTP Service Extension for Authentication</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc2595.txt">RFC2595</a></dt> + +<dd>Using TLS with IMAP, POP3 and ACAP</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc2645.txt">RFC2645</a></dt> + +<dd>On-Demand Mail Relay: SMTP with Dynamic IP Addresses</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc2683.txt">RFC2683</a></dt> + +<dd>IMAP4 Implementation Recommendations</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc2821.txt">RFC2821</a></dt> + +<dd>Simple Mail Transfer Protocol</dd> + +<dt><a +href="ftp://ftp.isi.edu/in-notes/rfc2822.txt">RFC2822</a></dt> + +<dd>Internet Message Format</dd> +</dl> + <!-- RFC2192 IMAP URL Scheme RFC2193 IMAP4 Mailbox Referrals RFC2221 IMAP4 Login Referrals --> +<hr /> +<table width="100%" cellpadding="0" summary="Canned page footer"> +<tr> +<td width="30%">Back to <a href="index.html">Fetchmail Home Page</a></td> +<td width="30%" align="center">To <a href="/~esr/sitemap.html">Site Map</a></td> +<td width="30%" align="right">$Date: 2002/07/28 09:23:04 $</td> +</tr> +</table> + +<br clear="left" /> +<address>Eric S. Raymond <a +href="mailto:esr@thyrsus.com"><esr@snark.thyrsus.com></a></address> +</body> +</html> -<HR> -<table width="100%" cellpadding=0 summary="Canned page footer"><tr> -<td width="30%">Back to <a href="index.html">Fetchmail Home Page</a> -<td width="30%" align=center>To <a href="/~esr/sitemap.html">Site Map</a> -<td width="30%" align=right>$Date: 2002/07/28 09:22:19 $ -</tr></table> - -<br clear="left"> -<ADDRESS>Eric S. Raymond <A HREF="mailto:esr@thyrsus.com"><esr@snark.thyrsus.com></A></ADDRESS> -</BODY> -</HTML> |