[Dovecot] ot: identifying TB IMAP issues

[Daniel Parthey]

Hij Voytek,

if the connection becomes stale, it might well be a network-related or client-side issue.

Have you ever heard of the ADSL MTU problem? If some router/firewall inbetween drops ICMP messages related to path-MTU-discovery, then the maximum transfer unit (MTU) might be wrong and larger packets might get dropped on their way which makes the TCP connection become stale.

The user's TCP segments need to be small enough so that a PPPoE header (8 Bytes) can be added to the packets without exceeding the default network MTU of 1500 Bytes, so the maximum recommnded TCP segment size for ADSL users is 1492 Bytes.

Read more about the maximum segment size (MSS) clamping issue here:

http://lartc.org/howto/lartc.cookbook.mtu-mss.html

Regards
Daniel