# of msgs, robustness

a. will eM handle xxxK messages in xxx of folders and sub-folders?
b. how robust is the database, e.g. what happens upon a power failure?


a. Yes, that is what eM Client has been designed for, unless like other email clients eM Client will continue to be fast even with hundreds of subfolders and tens of thousands emails.

b. Unless you will try to edit database manually it is very robust, most database failures are caused by using external tools or editing it directly.
For all cases we use our own internal backup tool.