[Dovecot] Cingular/ATT killing my IMAP/POP connections with bad TCP FIN packets?

[Adam McDougall]

On Mon, Mar 10, 2008 at 08:12:37PM -0400, Peter Tripp wrote:

  Hello all,
  
  I've got an issue I'm almost positive is not related to Dovecot, but was 
  wondering whether anyone else has had similar problems or could duplicate 

  Me: SYN
  Paradox: SYN, ACK
  Me: ACK
  Me: Client Hello
  Paradox: ACK
  Paradox: FIN, ACK
  Me: ACK
  Paradox: FIN, ACK
  Me: ACK
  -dead-
  
  http://duckies.org/~peter/damncingular.txt

I notice a 6-7 second delay between the first ACK and the first FIN,ACK.
Is your dovecot server perhaps unable to do a DNS lookup on the connecting
IP?  It would be very informative to see what the dovecot server is sending
(or not sending) including generated traffic such as DNS queries, if you 
can isolate that.  Is anything in the dovecot logs?  Wondering if it is 
related to something like tcp wrappers.