[Dovecot] imap / IPv6 problems?

[Egbert]

Hi, I have this intermittant problem.

When sending an email it *sometimes* takes ages before the process
finishes. The  process seems to hang in moving the message to the sent
items" folder". When I disable the IPv6 stack in the network config
(this is MS Windows 7), the hanging process immedialetely completes!
This makens me think that is has to do with the IP stacks. Another
observed effect is a long "rotating wheel" when just klicking on an imap
folder before the listing in the right pane updates. Here the same trick
solves the problem.

I use Thunderbird on W7 as client and have my mail (3 accounts) on a
remote mailserver. I have full control over that server which can become
handy... Th emailserver is Ubuntu 12.04 LTS with postfix and Dovecot
(2.0.19) from the standard repo's. My IPv6 connections is a native IPv6
from my ISP (xs4all.nl). I have no reason to think that the IPv 6
connecition itself is the problem.

Any advise to investigate this problem is welcome.

Egbert Jan, NL