Exchange Online Retires Basic SMTP Auth

[bbiankasc]

Use case

Exchange Online will permanently remove support for Basic authentication with Client Submission (SMTP AUTH) gradually beginning with a small percentage of submission rejections for all tenants on March 1st 2026 and reaching 100% rejections on April 30th 2026, (previously September 2025).

After April 2026, we 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.

Are there going to be support for OAuth?

Current Workaround

No known workaround.

Proposed Solution

OAuth support or additional documentation on the required configuration change.

Additional Information

Reference: https://techcommunity.microsoft.com/blog/exchange/exchange-online-to-retire-basic-auth-for-client-submission-smtp-auth/4114750

If the feature request is approved, would you be willing to submit a PR?

Yes with help

[nino-filigran]

Date has changed: https://techcommunity.microsoft.com/blog/exchange/updated-exchange-online-smtp-auth-basic-authentication-deprecation-timeline/4489835