I just saw this a bit late. I have NOD32 running with no problems, but I disabled the Email Protection > Append Note options turned off. I still have it set to scan incase one of my 200 users gets some scam email with phishing software. Those damned DHL invoice .exe's keep getting through Zimbra's built in scanner.
Mail | Dell 2950III | 2x Quad Core 5420 | 8gb RAM | 6x 146gb SAS RAID 0+1 | Red Hat 5.3 | Zimbra 6.0.10 Network Edition
Test | VMware ESXi Whitebox | Phenom II Black 3.2ghz | 12gb RAM | 6x 1tb SATA RAID 0+1 | CentOS 5.4 | FOSS, Not in use now