Am 06.06.2014 00:39, schrieb Joseph Tam: > Timo Sirainen <t...@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.
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
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