Exchange account disappears in Mail after install of Mojave

When I installed Mojave last week my Exchange (Office 365) email account stopped working in the Mail app. Unable to rectify the situation, I deleted the account and then readded it. Seemed like a reasonable solution.

When I re-add, it accepts my user name and password, and loads in the account and beings to download my emails. For 30 seconds. And then the account just disappears. Like I never even added it. I have tried to add it through every possible method I know how, and in each and every one of them, it starts to download, loads in my inbox and folders, and 30 seconds later, disappears. I had deleted and re-added my gmail, with no problems, and my Exchange account will load through the outlook app (ugh), but not through the Mail app (my preferred program of choice).

Not sure how to fix it, or if it's just a bug in Mojave. I've seen on reddit that I'm not the only one with this problem - just curious if anyone has found a solution.

(And for the record, problem exists on my iMac and MacBook, but not my husbands MacBook, which he had not upgraded to Mojave. So pretty sure Mojave is the problem here).