Troubleshooting SMTP Setup Error on Office365.com: Resolving EHLO Message Failure (535 5.7.139) - Authentication Unsuccessful, Basic Authentication Disabled

Error:

SMTP server 'smtp.office365.com' tested: Failure on EHLO message to server - 
535 5.7.139 Authentication unsuccessful, basic authentication is disabled.

Solution:

Cerberus utilizes Basic Authentication to integrate with an Office 365 (O365) SMTP Exchange server. Microsoft deprecated Basic Authentication as the default setting for O365 in October of 2023. However, you may be able to designate and allow a Windows account to authenticate on to O365 SMTP via Basic Authentication by following the steps in this Microsoft document:

Enable or disable authenticated client SMTP submission (SMTP AUTH) in Exchange Online