Updated June 12, 2025: We have delayed the Basic Auth removal from SMTP AUTH Client Submission to begin March 1st 2026 and complete by April 30th 2026 in order to give customers more time to adopt alternatives. Expect no further delays beyond this date. Please review the information below for more details.

Updated October 18, 2024: We have updated the SMTP AUTH Clients Submission Report in the Exchange admin center, adding the Authentication Protocol column to show if Basic auth or OAuth is being used to submit email to Exchange Online. The data will build up over the next 90 days. Thank you for your patience.

Today, we are announcing that 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 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.

Basic auth is a legacy authentication method that sends usernames and passwords in plain text over the network. This makes it vulnerable to credential theft, phishing, and brute force attacks. To improve the protection of our customers and their data, we are retiring Basic auth from Client Submission (SMTP AUTH) and encouraging customers to use modern authentication methods that are more secure.