Recently we had some users in one office who were unable to send mail attachments with Thunderbird - they sent OK with SMTP, but when Thunderbird tried to save a copy in the user's Sent folder, the operation failed.

When I looked on the wire, I could see something like this:

20 IDLE
+ Waiting for DONE
DONE
20 OK IDLE completed
21 append "Sent" (\Seen) {820767+}
Message-ID: <blahblah...
.. lots of base-64 text ..
i3X00+ZAg/gDi* BYE Autologout (idle for too long)
The logfile on the server I think logs "imapd[n]: Unexpected client 
disconnect.."

In that office, it looks like we have a real network problem - there are lots of TCP retransmits on larger packets, so the transaction is running afoul of IDLETIMER which is hardcoded at one minute in imapd.c. But that's making mail fail, rather than just running real slow like, for example, scp.

Since it seems to me that imapd is waiting for "DONE", not just network activity, I was wondering if it ever times out on a non-broken network - one that's just naturally slow, for instance. E.g. our sendmail has a byte limit of some 60Mb (some servers have no limit), so I could conceviably send a 50Mb attachment from home on my feeble 400kbps uplink, which would take much longer than 1 minute to write to Sent (I've yet to actually try that).

I do see quite a few "Unexpected client disconnect" messages in syslog in general, but have not yet joined all the dots together - I'm not sure if it's a general imapd issue, or an interaction with Thunderbird.


I was wondering if my interpretation of this is correct, and whether increasing IDLETIMER might be a good idea.

--
Andrew Daviel
TRIUMF
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