Mac mail will not sync with Exchange Server

Upgraded to Big Sur several days ago with no issues. However, yesterday I noticed that my personal email was not being updated. So i deleted the account and added it back in and all seemed to work fine. Today I noticed I had no new emails and logged into Outlook via the web and saw that it had not synced with the mail app and there were several emails.

After doing some research on the web to see if there was a fix, have not found one yet, I decided to do a little testing. So this is what I have so far.

I have 3 accounts that use Exchange servers, 1 is for personal mail and the other 2 are for corporate emails. I sent a test message out and the 2 corporate emails synced the emails into the inboxes without a problem. The personal email accounts did not. However, if I rebuild the personal email account, it then syncs with the server and I get all the emails.

Not sure what is going on. Also not sure what the differences, if any, are between types of Exchange servers.

Just wanted to put out some additional info on what is going on.

Before the upgrade to Big Sur this happened a couple of times and deleting and adding the email account solved the problem. Also no issues with the mail syncing with my iphone.

Steve