[Dovecot] Outlook 2007 & 2010 hangs in v2.2?

[Joseph Tam]

Timo Sirainen <tss at iki.fi> writes:

> Has anybody noticed Outlook 2007 & 2010 (but apparently not 2013)
> hanging IMAP connections with Dovecot v2.2 (but not v2.1) when they're
> FETCHing large mails? I can't think of any reasonable explanation for
> this.

It's a shot in the dark, but I had a problem with a different client,
where semi-large attachments was problematic.

It turned out to be a TCP scaling problem.  If a router/firewall drops
packets with a TCP scaling option set, the endpoints disagree on how many
outstanding non-ACK packets are allowed, resulting in timeouts.

 	http://support.microsoft.com/kb/935400
 	http://en.wikipedia.org/wiki/TCP_window_scale_option

The Microsoft KB does hint those versions of Outlook may be affected, but
I can't figure out why there would be a difference between Dovecot 2.1
and 2.2.

Joseph Tam <jtam.home at gmail.com>