We are using Sonicwall NSA 220. We have both Linux based system and windows based systems. On the Linux based systems we are using thunderbird as email-client and on the windows based systems we are using outlook as email-client.
On the Linux side:
I am unable to send email using thunderbird. Firewall logs show:
11 09/20/2013 11:09:34.096 Debug Network TCP connection abort received; TCP connection dropped 192.168.1.177, 26569, X0 (admin) mail-server:IP, 443, X1 TCP Flag(s): ACK RST
Download for emails is happening successfully without any problems.
When I use the firefox browser on the Linux box, The login goes through, however if I wish to send an email with attachment of 100KB or more, the connection times out. at the same time if I send a simple test-email, then the email goes through.
On the Windows side:
send/receive of emails using outlook as well as firefox/IE is going through without any errors.
Attempts to solve problem:
1. We had attempted to create a DMZ-zone a couple of days back, so to rule out any misconfiguration we have restored old Config from back as of 19-Aug.
Any suggestions on why this would be happening and if we can enable any addition logging to pin-point the problem.