Question : Issue with sending encrypted zip files through windows 2003 exchange servers

When sending encrypted zip file a bounce-back message is generated: There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.   5.5.0 smtp;551 Message contains an encrypted ZIP file (Mode: normal)>

Both sides are exchange 2k3.  We do have a sonicwall firewall on the other side, but I have carefully gone through and turned off all port 25 filtering.  There is nothing showing up in the log on the firewall either, and all messages are logged (we had some issues with the firewall blocking port 25 messages prior to turning off the gateway av/anti-spyware on port 25; and those all showed up in the log).  

Is there a default setting in exchange that disallows receipt of encrypted zip files?  Any guidance/help is much appreciated.

Answer : Issue with sending encrypted zip files through windows 2003 exchange servers

That is not an Exchange setting. It something outside of Exchange doing the blocking. AV, antispam, firewall, something like that. Exchange cannot do any attachment blocking on its own at the SMTP level.

Simon.