Well, I now have a NEW interesting event. ALL of my e-mails are now currently marked as Spam AND Trash! How exciting!
Have you tried:
Microsoft did have an update for this app. You can go to the Microsoft Store, click on the three dot (...) on the extreme right and pick "Downloads and Updates" and click the "Update" button to check and install. If you decide to go to step 2 below, that
will probably install the most updated version without doing this step. Note that your mail, if not deleted already, will repopulate in the app if you do other than step 1.
1) Resetting the app - Settings > Apps. Then find "Mail and Calendar" in the list, click on it and select (in blue) "advanced options" and select "Reset" further down
2) Removing (same as above but select "uninstall" from the choices)and reinstalling the app (called Mail and Calendar) from the Microsoft Store
3) When you add your account(s) back, if they are Google Mail, pick "Other Account, POP, IMAP" account instead of picking the Google Mail type and create them that way
Before you do anything else, be sure to go through all of the settings because they may change and will now be Microsoft default settings.
You should do send test emails to yourself to see if anything has changed. And be sure that all trash, spam or deleted boxes for each account are set as favorites (click on "More" in the list and then right click on the one your want to make a favorite)
so you can easily monitor what's going on.