We started recommending eM Client to our customers to use with SmarterMail. With it working seemingly well with EWS for email, contacts, calendar and tasks it seemed like a good idea. HOWEVER, we started getting one frantic call after another when every single user kept getting their eM Client database corrupted on a daily basis.
After some trial and error we finally tracked the issue to Drafts made in eM Client are trying to be synched to SmarterMail's Drafts folder and the corruption occurs. Disabling the auto-saving of Drafts in the eM Client Settings resolved the issue for our clients.
Note: this is an eM Client issue and not a SmarterMail issue but I figure there might be others who may experience the same problem so knowing why it is happening and how to fix it may be of great use to someone.