If you have enabled two-factor authentication (2FA) in Office 365, your emails might stop working or you can get errors like below when sending emails out from BillQuick:
This happens because BillQuick is not designed to interact with 2FA. However, Office 365 allows you to create a special account called App Password within your 2FA administration. Check out the Microsoft Support article on how to set this up. You may need to coordinate with the IT administrator who manages your Office 365.
After setting this up, you have to key in the App Password in BillQuick SMTP settings and it should work.