Verizon is one of the many Internet Service Providers that require you to authenticate when sending mail. The purpose of SMTP authentication is to reduce email spamming and abusive mailing behaviors.

If you've implemented multi-factor authentication, you should disable the default basic authentication to make sure attackers can't exploit it. Attackers will go after weaker credentials and passwords ...

Microsoft this week again appealed to organizations using Exchange Online to move away from using "Basic Authentication," reminding them that support for it will get dropped, starting on Oct. 1, 2022.