During the migration from on-premises Exchange to Exchange 365 here at Felinesoft, we're experiencing random certificate errors.
Run this program Office certificate fix and it will check for the message every half second and press "yes" when it appears.
To add this to your windows startup:
- Windows key + R
- Type
shell:startup
- Save Office certificate fix to the startup folder
- Double click to test the .exe (you'll likely have a windows warning, but press "More Info", and "Run", as this will only come up once)
Here is the error message it combats: