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550 5.7.30 Basic authentication is not supported for Client Submission

This error means a script or device tried to send mail through Exchange Online using a username and password (SMTP AUTH Basic Authentication). Microsoft disables this by default for existing tenants at the end of December 2026, with final removal to be announced in 2027. Fix it by switching the script to OAuth, or by routing through an approved relay.

Fix it now

  1. In the Exchange admin center, open the SMTP AUTH Clients Submission report and filter for Basic authentication to find every sender.
  2. Search your scripts for smtp.office365.com, Send-MailMessage, and stored mail credentials.
  3. Move each sender to OAuth. For internal-only bulk notices, evaluate Microsoft 365 High Volume Email. Hybrid campuses can relay through on-premises Exchange.
  4. Remove the stored password from the script and vault any remaining secret.
  5. Better yet: stop emailing passwords at all. Use first-time account claim so new users set their own credential.

Why this keeps happening

Basic Authentication sends a reusable password with every message, and Microsoft has been retiring it across Exchange Online for years. Scripts written before that change still carry the password and the old method. See the full Microsoft Deadline Calendar.

What breaks next

  1. NextEnd of Dec 2026
    SMTP AUTH Basic Authentication disabled by default for existing Exchange Online tenants (admins can re-enable for now)
    Who it hits: Scripts that email new-account notices via smtp.office365.com with a stored username and password
    Source: Microsoft Exchange Team blog: Updated SMTP AUTH Basic Authentication deprecation timeline (Jan 27, 2026)
  2. AnnouncedH2 2027
    Microsoft announces the final removal date for SMTP AUTH Basic Auth
    Who it hits: Same
    Source: Microsoft Exchange Team blog: Updated SMTP AUTH Basic Authentication deprecation timeline (Jan 27, 2026)

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Questions

Can we just turn Basic Auth back on?
For now, admins can re-enable it after the default change, but Microsoft will announce a final removal date in 2027. It's a delay, not a fix.
Why do identity scripts send email at all?
Many campus provisioning scripts email a username and temporary password to new students and staff. That's both the thing that breaks and a security risk.
Where does Microsoft say this error appears?
The Exchange Team's post retiring Basic auth for Client Submission says clients using Basic auth receive 550 5.7.30 Basic authentication is not supported for Client Submission once it is disabled. Microsoft's January 2026 timeline doesn't name the response for the end-of-December default change, so use the SMTP AUTH Clients Submission report to find senders now rather than waiting for the error.
Does this affect inbound mail or connectors?
No. It affects client submission (authenticated sending) only.

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