I just switched to MS Exchange email server and now eM Client reports a continuous stream of errors (see below). I am sending and receiving fine so it doesn’t seem to affect functionality. Do you know what I need to do to get it to stop reporting these errors?
Yes, fix the problem. 
The Log tab will tell you more about what the error is, or what was cancelled. Unfortunately there is not much mentioned on this forum about issues with Exchange servers. I think that may be because most of those happen with business users so they have access to Pro License Support. They report and have them resolved there rather than on this forum.
Unfortunately all the suggestions that could be tried with IMAP accounts don’t apply.
Maybe the log will point you in the right direction though.