What 550 5.7.1 means
The message Microsoft attaches to this code is “Delivery not authorized”, as written on its reference page. The first digit says how final it is: a 5xx reply is permanent for that message, so the sending server gives up and returns a bounce. The enhanced status 5.7.1 says what class of problem it is: recipient policy. The recipient's organization or mailbox has a rule that refuses the message. Nothing on the sender's side changes it.
Why it happens
The receiving organization has a rule that refuses this message: a block on the sender, a rule against mail from outside the tenant, an attachment or link type it does not accept, or a mailbox configured to take mail from known contacts only. The rule belongs to the recipient, so there is nothing on the sending side to repair.
What to do first: Recipient organization policy (distribution group restrictions, DBEB).
Why warming does not fix this
Warming builds sender reputation. 550 5.7.1 in this form is a recipient policy problem, and no amount of engagement history changes it. Fix the cause and the bounce stops; warming is for what comes after, when the mail is accepted and the question becomes which folder it lands in. See how warming works for that part.
How to fix it, in order
- Nothing to fix on your side; the recipient's organization refused the message by rule
- Remove the address from sequences and, where it matters, ask the recipient for an alternative
Related codes
- 550 5.7.1 (Gmail): likely unsolicited email
- 550 5.7.1 (Gmail): rate limited
- 550 5.7.1 (Gmail): policy prohibits the email
- 550 5.7.1 (Gmail): IP not authorized to send directly
- 550 5.7.1 (Gmail): very low sending domain reputation
More on Microsoft 365
- Microsoft 365 emails going to junk: the trace in order: headers, Message Trace, quarantine, SNDS
- Microsoft bulk sender requirements: the 5 May 2025 authentication rules and the 550 5.7.515 rejection
- Microsoft 365 sending limits: the documented recipient and message rate limits
Questions about 550 5.7.1
What does 550 5.7.1 mean?
Microsoft returns 550 5.7.1 with the message "Delivery not authorized": delivery not authorized. The recipient's organization or mailbox has a rule that refuses the message. Nothing on the sender's side changes it.
Is 550 5.7.1 a hard bounce or a soft bounce?
A hard bounce for that message: the 550 reply is permanent, and the message is not retried. Whether the address should be removed depends on the cause: here the fix is on the sending side, not the list.
How do I fix 550 5.7.1?
Recipient organization policy (distribution group restrictions, DBEB). Microsoft's own reference for the code is linked on this page.
Does email warmup fix 550 5.7.1?
No. 550 5.7.1 in this form is a recipient policy problem, and warming builds reputation, which is not what is failing here. Fix the cause and the bounce stops.