i've had the same issue on mac os 10.4.10 ppc (g4/450 cube with 1.5Gb ram) running 4.5.6 OSS. it's a slow box, but it runs zimbra well for a small domain of < 10 users.
i modified the interval to 240 sec and my problem went away (180 didn't work for me). this was a serious issue as my system's hd filled to 100% capacity with messages stuck in the /opt/zimbra/clamd/tmp directory, i think it was. i purged the tmp files and turned off av until i read about this solution.
-geo |