Am 06.06.2014 00:39, schrieb Joseph Tam:
Timo Sirainen tss@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_optionThe 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.
TCp scaling is a problem since many years and well known for delivery problems with MTA's if there are broken network devices between both sides
just disable it *anywhere* and be happy