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

Reindl Harald h.reindl at thelounge.net
Thu Jun 5 22:41:43 UTC 2014

Am 06.06.2014 00:39, schrieb 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.

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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