Information about MAC client:
1) Mac OS X Version 10.4.9
Intel Core 2 Duo Processor
Mail Version 2.1.1 (752.3)

2) Mac OS X Version 10.4.9
PowerPC G5
Mail Version 2.1 (752/752.2)

ANSWER
Disabling the SSL reuse option helps resolve the
problem on Mac OS Mail client for SSL imaps connection.

no ssl settings reuse <VHOST>