After being plagued by a repeated message from the Windows 10 Mail app about something being wrong with my account, I finally decided to troubleshoot it.
I click on Fix Account, a dialog box that looks like it wants to sign me back into Office 365 pops up. Then another box pops up and simply states “Something went wrong”.
Super useful.

A quick Google search to something so generic leads to the usual laundry list of overly complicated “fixes” that no one confirms actually works.

Lately I’ve been taking the shotgun blast approach because I just don’t have the time to perform 50+ steps to fix what should be a small issue.

Go to the Settings app, click on Apps, scroll down to Mail and Calendar, click Advanced Options, scroll down and click reset, click reset again.
Open Mail, re-add your account, WHAM, working in 5 minutes.