After 2 horrible weeks after the migration from v15 to v16 we decided to downgrade to v15 and all the problems were solved.
Smartertools support guy (Von) with more than 8 years of experience solving problems, only blame my hardware, disk bottlenecks, technical stuff that sucks.
We are a corporate mail hosting supplier, with more than 15 years using SmarterTools, especially SmarterMail, we lost large customers because the migration, all of our customers lost their sent items and smartertools support want us to have 2 weeks of backups for more than 800 GB of data, they only said, sorry, if you don't have a backup, there's nothing we can do and was not our responsibility.
We strongly recommend DO NOT UPGRADE or INSTALL V16.
After downgrade, we lost a lot of security configuration, we are having do do it again manually, and smartertools? Nothing to say.
Are you willing to pay annually for upgrades and this happens, we will not pay anymore for upgrades, V15 is stable and works fine, uhh but we have ActiveSync users, and we have to renew all the package, you cannot renew only ActiveSync, intelligent move from SmarterTools to force angry customer to pay annually.