Exchange Online to Retire Basic Auth for SMTP AUTH by 2025 | M365 Admin

In September 2025, Exchange Online will be retiring Basic Auth for Client Submission (SMTP AUTH). This means that applications and devices using Basic Auth will no longer be supported and must switch to OAuth or other alternatives for authentication. This move is intended to improve the security of customer data and protect against credential theft, phishing, and brute force attacks. To prepare, users are advised to follow the steps provided to authenticate email connections using OAuth if their client supports it. If not, alternative options should be explored.

A timeline has been provided for the retirement of Basic Auth, with updates and alerts to be sent to tenants who are still using it in preparation for the change. From September 2025, Basic Auth will be disabled and any clients or apps still using it will receive an error message. By switching to modern authentication methods such as OAuth, users can ensure the continued security and accessibility of their email submissions via Exchange Online.

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