Warnings about concurrent runs.

svn path=/trunk/; revision=98

2 files changed, 44 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index fcdc8653..05432611 100644
--- a/NEWS
+++ b/NEWS
@@ -4,6 +4,45 @@ To-do list:
 
 Option to enable EMACS-like user folder versioning on each run.
 
+The IMAP support is naive.  Chris Newman, one of the IMAP maintainers,
+criticized it as follows:
+------------------------------- CUT HERE -----------------------------------
+On Wed, 18 Sep 1996, Eric S. Raymond wrote:
+> 1. I do one one SELECT, at the beginning of the fetch.  
+> 
+> 2. I assume that I can pick an upper bound on message numbers from the EXISTS
+>    reponse.
+
+Correct.
+
+> 3. If there is an UNSEEN nnn trailer on the OK response to SELECT, I assume
+>    that the unseen messages have message numbers which are the nnn consecutive
+>    integers up to and including the upper bound.
+> 
+> 4. Otherwise, if the response included RECENT nnn, I assume that the unseen
+>    messages have message numbers which are the nnn consecutive integers up to
+>    and including the upper bound.
+
+These will only work if your client is the only client that accesses the
+INBOX.  There is no requirement that the UNSEEN and RECENT messages are at
+the end of the folder in general.
+
+If you want to present all UNSEEN messages and flag all the messages you
+download as SEEN, you could do a SEARCH UNSEEN and just fetch those
+messages.
+
+However, the proper thing to do if you want to present the messages when
+disconnected from the server is to use UIDs.  To do this, you remember the
+highest UID you have (you can initialize to 0), and fetch everything with
+a higher UID.  Ideally, you shouldn't cause the SEEN flag to be set until
+the user has actually seen the message.  This requires STORE +FLAGS SEEN
+for those messages which have been seen since the last update.
+
+The key thing to remember is that in IMAP the server holds the
+authoratative list of messages and the client just holds a cache.  This is
+a very different model from POP.
+------------------------------- CUT HERE -----------------------------------
+
 IMAP extensions for secure challenge-response.
 
 Recode POP2 to use the same driver/method strategy as POP3/IMAP, so 
@@ -16,6 +55,8 @@ driver to SMTP.  (This requires that we find a POP2 server to test with.)
 
 * Ported to QNX (see the Makefile).
 
+* Warn users that running concurrent instances of popclient is a bad idea.
+
 3.1:
 
 * MDA arguments are now dumped when using the -V option.
diff --git a/fetchmail.man b/fetchmail.man
index 53b27e61..9ddbb514 100644
--- a/fetchmail.man
+++ b/fetchmail.man
@@ -559,6 +559,9 @@ default configuration file
 default location of file associating hosts with last message IDs seen
 (used only with newer RFC1725-compliant servers supporting the UIDL command).
 .SH BUGS
+Running more than one concurrent instance of
+.I popclient
+on the same mailbox may cause messages to be lost or remain unfetched.
 .PP
 When using POP2, the --smtphost option doesn't work, and mail headers
 are not rewritten to enable replies as described under --norewrite.