Microsoft 365 Is Switching Off Basic SMTP Sign-In: What Will Stop Working?

At the end of December 2026, Microsoft 365 stops letting devices and apps send email with just a username and password. Your own Outlook keeps working. What stops is the equipment and software that sends email by itself: the office scanner, the website’s contact form, the accounts package that emails invoices. Nothing warns you first; the emails just stop.

Email Fix is an independent service and is not connected with Microsoft.

When a scanner or app sends email through Microsoft 365, it usually connects to smtp.office365.com and signs in with a mailbox’s username and password. Microsoft calls this Basic authentication for SMTP AUTH. It is replacing it with a more secure sign-in called OAuth, or modern authentication.

At the time of writing (last checked 9 October 2026), Microsoft’s timeline is:

1. Now until December 2026: nothing changes.
2. End of December 2026: basic sign-in for sending is switched off by default on existing Microsoft 365 accounts. Anything still using it is refused. An administrator can switch it back on as a stopgap.
3. New Microsoft 365 accounts created after December 2026 won’t have it at all.
4. Second half of 2027: Microsoft will announce the date it is removed for good. After that there is no stopgap.

Microsoft has moved this timeline before, so check its current announcement before planning around an exact day. Planning to be finished by early December is safe either way.

In a typical small office, look at:

• Scanners and copiers that “scan to email”. These are the most common casualty, often set up years ago by a supplier.
• The website’s contact form, if it sends through your Microsoft 365 mailbox using an email plugin.
• Accounts, booking and CRM software that emails invoices, reminders or confirmations from your address.
• Alarms, CCTV, door entry and building systems that email alerts.
• Scripts and older programs that send reports or backups by email.
• Older email programs and phones that can only sign in with a password.

What you will see afterwards: the scanner says “send failed”, the form appears to work but no email arrives, or the software logs this error:

550 5.7.30 Basic authentication is not supported for Client Submission.

My page on 550 5.7.30 explains that error in full.

1. Make a list, by walking round. Every device and program that sends email without a person pressing Send. Ask whoever set up the scanner and the website.
2. Look at each one’s email settings. If it uses smtp.office365.com, port 587, and a username and password, it is affected.
3. Ask your Microsoft 365 administrator for the SMTP AUTH clients report. It is in the Exchange admin centre under the mail flow reports, and shows which mailboxes are being used to send with a password. A mailbox you didn’t expect is usually a device someone forgot.
4. Note which mailbox each one signs in with. Often it is one person’s mailbox. If that person leaves, or their password changes, the device stops too.

1. Switch it to modern sign-in. Look in its settings for “OAuth” or “Sign in with Microsoft”. Most website email plugins and newer scanners have it. This is the best fix where it exists.
2. Send through a Microsoft 365 connector (SMTP relay). Your administrator sets up a connector so devices at your office’s fixed internet address can send without signing in. This suits scanners and copiers in one office.
3. Send through a separate email sending service. The device or website sends through a service built for it. It needs its own records added to your domain.
4. Replace it, if it is old and can do neither.
5. Switch basic sign-in back on, as a stopgap only. It buys time until Microsoft’s final date, which has not been announced yet. Put the real fix in the diary.

If you choose a connector or a sending service, add it to your SPF record, or its emails may start going to spam instead of being refused. My guide to SPF, DKIM and DMARC explains why.

After changing anything, send a test from it to a personal Gmail address: a scan, a form enquiry, a test invoice. The email should arrive, and in Gmail, under the three dots and “Show original”, SPF and DKIM should both show PASS. For website forms, my guide to contact forms that stop sending has more checks.

• Scanner stopped emailing?, for the four ways to fix scan-to-email.
• 550 5.7.30: Basic Authentication Not Supported, if something has already stopped.
• Website contact form not sending emails?, if it is your website.
• What is SPF, DKIM and DMARC?, for the records a new sending route needs.

Need help fixing this?

I provide:

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Tell me what in your office sends email, and I’ll find what will stop in December and set up a sending route that keeps working.