Sorry, this doesn't belong to Packages: Extra... Somehow I didn't realize that courier-mta had been moved to community.

And moved ;)

Removing gamin forcibly is a workaround. But this leads to many error messages in mail.log (and probably feature limitations related to concurrent mail folder access). However, still better than lags and disconnections of IMAP clients.

Tried the fam package from AUR. Unfortunately, it didn't work for me. The fam daemon crashed each time Courier tried to connect to it.
famd: FileSystemTable.c++:179: static void FileSystemTable::create_fs_by_name(): Assertion `root' failed.

This is what it looks like in Courier's log:
Apr 24 20:40:53 charon imapd: Failed to create cache file: maildirwatch (<<mail address here>>)
Apr 24 20:40:53 charon imapd: Error: Input/output error
Apr 24 20:40:53 charon imapd: Check for proper operation and configuration
Apr 24 20:40:53 charon imapd: of the File Access Monitor daemon (famd).

This message is displayed by Thunderbird:
Alert from account Charon - Andrej: Filesystem notification initialization error -- contact your mail administrator (check for configuration errors with the FAM/Gamin library)

So gamin was probably the only working choice ... till now. Now it freezes client connections nearly forever. (If I understand it well, the first IMAP connections work somehow and just lag for a few seconds, but they don't get closed, so the communication soon hits the limit on the number of connections per client and that's when everything stops working.)

Can't reproduce with my own production courier-imap installation. Is courier-mta any different? Anyhow, whose bug is this actually? Arch, courier, gamin?

courier-mta is IMO not that different. It includes some extra servers (such as ESMTP). Only the IMAP server is affected by this bug.
I have no idea whose bug this is. The IMAP part of Courier just stopped working after today's pacman -Syu. I even rebooted the server, but that didn't help either.

BTW, you may *not* see this bug if you don't use a client with IDLE capabilities. If you turn on IDLE support in Thunderbird, the bug should get exposed.

Update: FAM works and it doesn't crash. The FAM problem was caused by a bad symlink in my /etc directory, as described here: https://bugs.archlinux.org/task/29605

Gamin still fails the same way:
Apr 24 23:41:53 charon imapd: FAMPending: timeout

Once I uninstall Gamin and install FAM, Courier-MTA works fine. (Samba probably wouldn't work, but fortunately I don't use it right now.)

Now basically: wat do? This doesn't sound like a packaging problem. You should post this to upstream.

Yes, maybe I should... Some people might have already done that (linked in the bug report), but I'm not sure whether it is the same bug or not. Those bug reports date back to November 2011, yet my courier + gamin setup worked perfectly fine till last week.

The way I see it, if no big changes and/or patches have been recently added to gamin / courier-mta, perhaps you can close/defer this bug. My current FAM configuration works fine. There are currently no votes for the bug (but mine), so this problem might well be unrelated to packaging.

gamin in Arch was last updated in Nov. courier-mta was updated in Feb. This is surely no recent change of this packages. However, updates of other packages might have affected their behaviors.

Closing this for now, please reopen if you have new infos on this.