We use GMail (G-Suite) for outbound mail. Three days ago, we started getting:
authentication failure [SMTP: Invalid response code received from SMTP server while sending email. This is often caused by a misconfiguration in Outbound Email settings. Please verify the settings at Administer CiviCRM >> Global Settings >> Outbound Email (SMTP). (code: 535, response: 5.7.8 Username and Password not accepted. Learn more at 5.7.8 https://support.google.com/mail/?p=BadCredentials n3sm11135782pff.102 - gsmtp)]
We've verified (ad nauseam) that the Username and Password are correct. We can use them to send and receive through GMail just fine. However, we can no longer send with Outlook, either.
How can I find out why the Username and Password are no longer accepted?