ZeroSMTP — a free SMTP relay that still accepts basic auth
Your printer, scanner or app stopped sending email through Microsoft 365? You’re most likely hitting the Basic authentication shutdown. This site explains what happened, lists every way to fix it, and documents one free option among them.
535 5.7.139 Authentication unsuccessful, basic authentication is disabled
If that’s the error you’re seeing, start with Exchange Online SMTP AUTH migration.
Start here
| If you… | Go to |
|---|---|
Got an authentication error from smtp.office365.com |
Exchange Online SMTP AUTH migration |
| Need to know what else in your environment will break | What breaks: affected systems |
| Have a printer or MFP to reconfigure | Printer scan-to-email setup by brand |
| Manage Windows Server / IIS / Exchange | Windows Server guide |
| Manage Linux servers | Linux · system-wide relay |
| Are sending from an app or script | Code examples in 15 languages |
| Have it failing or timing out | Troubleshooting |
| Just want the short answers | FAQ |
What is happening
Microsoft is retiring Basic authentication (username + password) for SMTP AUTH in Exchange Online. Per Microsoft’s updated timeline, it is disabled by default on existing tenants at the end of December 2026, unavailable by default for tenants created after that, with final removal announced in the second half of 2027.
Devices that can run OAuth 2.0 can be updated. Older printers, scanners, NAS units and line-of-business software generally cannot — and for many of them no firmware update will ever exist.
What ZeroSMTP is
A free SMTP relay at mx.msgwing.com that still accepts a plain username
and password over TLS. For a device with no OAuth path, migrating means
changing three fields:
| Setting | From | To |
|---|---|---|
| Server | smtp.office365.com |
mx.msgwing.com |
| Port | 587 | 587 (STARTTLS) or 465 (SSL/TLS) |
| Credentials | Microsoft 365 account | free @msgwing.com account |
The trade-off, stated plainly: mail is sent from an @msgwing.com
address, not your own domain
(why),
and there is a 200 emails/day limit.
That makes it a good fit for scan-to-email, device and backup alerts, monitoring notifications, homelabs, schools and small offices — anywhere the message just needs to arrive. It is not the right answer for customer-facing mail or anything that must come from your company domain. The migration guide covers the options that are, including Microsoft’s own.
Get started
- Register a free account at msgwing.com.
- Copy the generated
@msgwing.comusername and password. - Point your device or app at
mx.msgwing.comon port 587 with STARTTLS.
Full quickstart, 15 language examples and setup guides are in the GitHub repository.
Service status is checked automatically every 6 hours — see the live check. Questions or corrections: open an issue.