On Apr 15, 2024, Microsoft Exchange Team announced that Exchange Online will permanently remove support for Basic authentication with Client Submission (SMTP AUTH) in September 2025 (exact date to be determined). After this time, applications and devices will no longer be able to use Basic auth as an authentication method and must use OAuth when using SMTP AUTH to send email.
During September 2025, Exchange Online will remove support for Basic auth with the Client Submission (SMTP AUTH) endpoints:
smtp.office365.com
smtp-legacy.office365.com
Once Basic auth is permanently disabled, any clients or apps connecting using Basic auth with Client Submission (SMTP AUTH) will receive this response:
550 5.7.30 Basic authentication is not supported for Client Submission.
Hi, a little update with a new deadline from Microsoft : It seems that the end of support of basic auth has been postpone to April 2026 : https://techcommunity.microsoft.com/blog/exchange/exchange-online-to-ret...