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| -rw-r--r-- | fetchmail.man | 54 |
1 files changed, 38 insertions, 16 deletions
diff --git a/fetchmail.man b/fetchmail.man index 987b01f0..7001fb62 100644 --- a/fetchmail.man +++ b/fetchmail.man @@ -615,17 +615,47 @@ server user names `golux', `hurkle', and `snark'. It further specifies that `golux' and `snark' have the same name on the client as on the server, but mail for server user `hurkle' should be delivered to client user `happy'. -.PP -Local names can also be used to administer a mailing list from the +.SH THE USE AND ABUSE OF MULTIDROP MAILBOXES +Use the multiple-local-recipients feature with caution -- it can bite. +The fundamental problem is that by having your server toss several +peoples' mail in a box, you have thrown away potentially vital +information about who each piece of mail was actually addressed to. +This can't always be deduced from the headers, especially when mailing +lists are involved. +.SS Good Ways To Use Multidrop Mailboxes +Multiple local names can be used to administer a mailing list from the client side of a \fIfetchmail\fR collection. Suppose your name is \&`esr', and you want to both pick up your own mail and maintain a mailing list called (say) "fetchmail-friends", and you want to keep the alias -list on your client machine. On your server, you can alias -\&`fetchmail-friends' to `esr'; then, in your \fI.fetchmailrc\fR, declare -\&`to esr fetchmail-friends here'. Then, when mail including `fetchmail' -in any of its recipient lines line gets fetched, the alias will be -appended to the list of recipients your SMTP listener sees. Therefore -it will undergo alias expansion locally. +list on your client machine. +.PP +On your server, you can alias \&`fetchmail-friends' to `esr'; then, in +your \fI.fetchmailrc\fR, declare \&`to esr fetchmail-friends here'. +Then, when mail including `fetchmail-friends' in any of its recipient +lines gets fetched, the list name will be appended to the list of +recipients your SMTP listener sees. Therefore it will undergo alias +expansion locally. (Be sure to include `esr' in the local alias +expansion of fetchmail-friends, or you'll never see mail sent only to +the list!) +.PP +This trick is not without its problems, however. You'll begin to see +this when a message comes in that is addressed only to a mailing list +you do \fInot\fR have declared as a local name. Each such message +will feature an `X-Fetchmail-Warning' header which is generated +because fetchmail cannot find a valid local name in the recipient +addresses. Such messages default (as was described above) to being +sent to the local user running +.IR fetchmail , +but the program has no way to know that that's actually the right thing. +.SS Bad Ways To Abuse Multidrop Mailboxes +Multidrop mailboxes and +.I fetchmail +serving multiple users in daemon mode do not mix. The problem, again, is +mail from mailing lists, which typically does not have an individual +recipient address on it. If you have multiple local names declared, +.I fetchmail +cannot know which to send it to! It will only go to the account +running fetchmail (probably root). .SH EXIT CODES To facilitate the use of .I fetchmail @@ -717,14 +747,6 @@ to the mailserver. This creates a risk that name/password pairs might be snaffled with a packet sniffer or more sophisticated monitoring software. .PP -Retrieval and forwarding from multi-drop server mailboxes is at most -as reliable as your mail server host's DNS service. Each host address -part in each message of a multi-drop mailbox is looked up through DNS -to see if it's an alias of the mail server (the method \fIwill\fR -catch equivalences created by MX records). If it is an alias of the -server, but the lookup fails due to network congestion or a crashed -server, forwarding will not get done correctly. -.PP Send comments, bug reports, gripes, and the like to Eric S. Raymond <esr@thyrsus.com>. .SH SEE ALSO |