Implement OAuth support for Microsoft Exchange Online

Problem/Motivation

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.

Further information

• Microsoft Exchange Online announcement
• Microsoft documentation (Authenticate an IMAP, POP or SMTP connection using OAuth)