💡 Our Technical Review in summary
Summary
- Microsoft has refined the deprecation timeline for Basic Authentication in Exchange Online SMTP AUTH (Client Submission) to provide more transition time.
- The previous deadline (March 2026) is replaced by a phased rollout: through December 2026, service remains unchanged; starting late December 2026, it will be disabled by default for existing tenants.
- For new tenants created after December 2026, Basic Auth for SMTP will be unavailable by default.
- A final removal date for Basic Auth will be announced in the second half of 2027.
Impact
- Service Disruption: Any legacy applications, devices (such as printers/scanners), or scripts relying on a simple username and password to send email via SMTP will fail once Basic Auth is disabled.
- Security: Moving to OAuth mitigates risks associated with credential theft, phishing, and brute-force attacks inherent to legacy authentication.
- Tenant Configuration: After December 2026, administrators of existing tenants will still have the option to manually re-enable Basic Auth if necessary, but this will be a temporary workaround.
- Reporting: The Exchange admin center (EAC) now includes an updated SMTP AUTH Clients Submission Report that identifies whether clients are using Basic Auth or OAuth.
Action Required
- Audit Usage: Immediately review the “SMTP AUTH Clients Submission Report” in the Exchange admin center. Use the new “Authentication Protocol” column to identify which devices or accounts are still using Basic Auth.
- Upgrade to OAuth: Update application configurations and device firmware to support OAuth 2.0 for SMTP connections where possible.
- Identify Legacy Gaps: For systems that cannot support OAuth, plan to migrate to one of the following alternatives:
- Microsoft 365 High Volume Email (HVE): Currently in Public Preview, designed for high-volume internal mail.
- On-premises Relay: Use an Exchange Server on-premises with a Receive connector (for hybrid environments).
- Third-Party Solutions: Utilize a third-party SMTP relay service that supports legacy authentication if required.
- Prepare for 2027: Use the extended runway to phase out all Basic Auth dependencies before the final removal date is announced in late 2027.
Microsoft Official Update
Service: N/A
Category: planForChange
Severity: normal
Updated January 27, 2026: Based on customer feedback and visibility into adoption progress, we are refining the Exchange Online SMTP AUTH Basic Authentication Deprecation timeline to provide clearer milestones and additional runway.
- Now to December 2026: SMTP AUTH Basic Authentication behavior remains unchanged.
- End of December 2026: SMTP AUTH Basic Authentication will be disabled by default for existing tenants. Administrators will still be able to enable it if needed.
- New tenants created after December 2026: SMTP AUTH Basic Authentication will be unavailable by default. OAuth will be the supported authentication method.
- Second half of 2027: Microsoft will announce the final removal date for SMTP AUTH Basic Authentication.
We will provide detailed information in a follow up Message Center Post.
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.
The SMTP AUTH Basic Authentication Deprecation has been put on hold. In 2027, Microsoft will announce the final removal date for SMTP AUTH Basic Authentication.
Once Basic Auth is removed from SMTP AUTH, 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.
[When this will happen:]
The removal of Basic Auth from SMTP AUTH Client Submission has been put on hold (previously beginning March 1st, 2026, and completing April 30th, 2026).
[How this will affect your organization:]
The SMTP AUTH Clients Submission Report in the Exchange admin center has been updated to show if Basic auth or OAuth is being used to submit email to Exchange Online.
The removal of Basic Auth from SMTP AUTH Client Submission has been put on hold (previously beginning March 1st, 2026, and completing April 30th, 2026).
[What you need to do to prepare:]
The removal of Basic Auth from SMTP AUTH Client Submission has been put on hold (previously beginning March 1st, 2026, and completing April 30th, 2026)
If your client supports OAuth, follow these steps: Authenticate an IMAP, POP or SMTP connection using OAuth
If your client doesn’t support OAuth and you must use Basic Auth with Client Submission (SMTP AUTH), you will need to switch to one of the following alternatives following the timeline that will be announced in 2027 (previously April 2026):
• If you are using basic authentication with Client Submission (SMTP AUTH) to send emails to recipients internal to your tenant, you can use Microsoft 365 High Volume Email. Please visit this site to learn more: Manage high volume emails for Microsoft 365 Public preview
• If you have an Exchange Server on-premises in a hybrid configuration, you can use Basic auth to authenticate with the Exchange Server on-premises or configure the Exchange Server on-premises with a Receive connector that allows anonymous relay on Exchange servers. Please visit this site to learn more: Allow anonymous relay on Exchange servers
Regardless of the volume of email, if you must use Basic auth to send email with Exchange Online, then you must use one of the alternatives or a 3P solution.
We understand that this change requires some adjustments, but we believe that this is a necessary step to enhance the security and reliability of our email service and your data.
