This is a know issue.
I have a ticket open on that and SmarterTools said me that they are working on a FIX....
No ETA yet
Gabriele Maoret - Head of SysAdmins at SERSIS
Currently manages 6 SmarterMail installations (1 in the cloud for SERSIS which provides services to a few hundred third-party email domains + 5 on-premise for customers who prefer to have their mail server in-house)