550 5.7.1 Microsoft bounce: delivery not authorized
What 550 5.7.1 means
The recipient accepts mail only from authorized senders, such as members of a distribution group, and the sender is not on that list.
Message text
Delivery not authorized
Common causes of 550 5.7.1
- Sender is not an authorized sender for the recipient or distribution group
- A transport rule matched and rejected the message
How to fix 550 5.7.1
- Ask the recipient or group owner to add you as an authorized sender.
- If you administer the recipient tenant, review the transport rules that matched.
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How to read 550 5.7.1
The first part, 550, is the SMTP reply code. Requested action not taken, mailbox unavailable: the mailbox does not exist, is not allowed, or the message was refused for policy reasons. Replies that start with 4 are temporary and replies that start with 5 are permanent (RFC 5321 §4.2.1).
The second part, 5.7.1, is an enhanced status code (RFC 3463 §2) written class.subject.detail. Class 5 is a Permanent failure (5xx): the command was rejected and the sender should not repeat it unchanged (RFC 5321 §4.2.1; RFC 3463 §2).. Subject 7 is security or policy: authentication, authorization or policy refused the message. The detail number refines the subject, and providers may define details of their own, which is why one code can read differently at Gmail, Microsoft and Yahoo.
Do not keep resending the same message: a permanent failure repeats until the cause is fixed. Correct the cause, then send a new message.
Official source: learn.microsoft.com. Last verified 2026-10-20.
Related guides
- How to create an SPF record (syntax and examples)
- How DKIM works and how to publish a DKIM record
- How to set up a DMARC record, from p=none to p=reject
Related codes
- 5.7.1 SMTP: delivery not authorized
- 550 5.7.1 Gmail: likely unsolicited
- 550 5.7.1 Microsoft: unable to relay
- 530 5.7.1 Microsoft: not authenticated
- 5.7.0 SMTP: security status
- 5.7.23 SMTP: SPF validation failed
FAQ
What does 550 5.7.1 mean?
The recipient accepts mail only from authorized senders, such as members of a distribution group, and the sender is not on that list. This is a permanent failure.
How do I fix 550 5.7.1?
Ask the recipient or group owner to add you as an authorized sender. If you administer the recipient tenant, review the transport rules that matched.
Is 550 5.7.1 permanent, and should I retry?
550 5.7.1 is a permanent failure, so retrying the same message will fail again. Fix the cause first, then send a new message.