550 5.7.708 Service unavailable. Access denied, traffic not accepted from this IP
Microsoft 365 blocked the tenant's outbound mail
Seen in Microsoft 365, Exchange Online (outbound)
Most of this tenant's recent outbound mail looked suspicious, so Microsoft restricted its ability to send (5.7.705 and 5.7.708 are the same block).
Common causes
- A new or trial tenant sent a large volume before building any reputation.
- Compromised accounts in the tenant sent spam or phishing.
- An open relay or misconfigured connector let outsiders send through the tenant.
How to fix it
- Find and secure compromised accounts: reset passwords, revoke sessions and enforce MFA.
- Close any open relay connectors and review outbound connector settings.
- Once it is clean, open a request with Microsoft support to lift the restriction.
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Related errors
- 550 5.4.1 Recipient address rejected: Access denied · Microsoft 365 rejected an unknown recipient at the edge
- 530 5.7.57 Client not authenticated to send anonymous mail during MAIL FROM · The app sent to smtp.office365.com without logging in
- 535 5.7.139 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Tenant · Microsoft 365 refused the SMTP AUTH login
- 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