535 5.7.139 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Tenant
Microsoft 365 refused the SMTP AUTH login
Seen in Microsoft 365 (smtp.office365.com), Outlook.com, apps and printers using SMTP AUTH
Exchange Online rejected the SMTP AUTH login; the text after the comma says why (SMTP AUTH disabled, basic authentication disabled, or blocked by security defaults).
Common causes
- SMTP AUTH is turned off for the tenant or the mailbox, which is the default for new tenants.
- Basic authentication (username and password) is blocked; Microsoft is retiring it for SMTP AUTH.
- Security defaults or a Conditional Access policy blocks legacy authentication for the account.
How to fix it
- Enable SMTP AUTH for just the sending mailbox: Set-CASMailbox -Identity user@example.com -SmtpClientAuthenticationDisabled $false.
- Move the app to OAuth 2.0 for SMTP, or to Microsoft Graph sendMail.
- For devices that cannot do modern authentication, use direct send or an SMTP relay connector instead.
Got a different message? Paste it into the error explainer.
Related errors
- 550 5.4.1 Recipient address rejected: Access denied · Microsoft 365 rejected an unknown recipient at the edge
- 550 5.7.708 Service unavailable. Access denied, traffic not accepted from this IP · Microsoft 365 blocked the tenant's outbound mail
- 530 5.7.57 Client not authenticated to send anonymous mail during MAIL FROM · The app sent to smtp.office365.com without logging in
- 550 5.7.520 Access denied, Your organization does not allow external forwarding · Automatic forwarding to an outside address is blocked
- 550 5.1.8 Access denied, bad outbound sender · The sending account was blocked for spam
- 451 4.7.500 Access denied, please try again later · Microsoft 365 is temporarily throttling the sending IP
- 552 5.2.2 The recipient's inbox is out of storage space · The recipient's mailbox is full
- 552 5.3.4 Your message exceeded Google's message size limits · The message is larger than the server accepts
- 535 5.7.8 Username and Password not accepted · The SMTP login was rejected
- 450 4.2.0 <user@example.com>: Recipient address rejected: Greylisted · The message was greylisted; it will be accepted on retry
- 553 5.7.1 <user@example.com>: Sender address rejected: not owned by user · You logged in as one user but sent as another address
- 530 5.7.0 Must issue a STARTTLS command first · The server requires TLS before it accepts mail