I think I might have found a bug. I did a search and couldn't find the specific issue that pertains to my situation, so I figured I'd post here. This is on a new Zimbra installation.
When we go to Global Setting > Attachments and try and block zip files it seems to crash the server after the first email is sent that actually contains the zip attachment in it. Once that email is sent, it also shuts down the Antispam and Antivirus services. Once those are shut down, the server cannot send/receive email. The zip extension needs to be removed from the attachments tab and then the server needs to be rebooted before things will come back to life. Once rebooted and all services are running, the server will send and receive once again.
Anyone else seeing this?