550 5.7.708 error (Outlook / Microsoft): Traffic from this IP is not accepted
Microsoft 365 rejects traffic from this IP because of its reputation, often on shared or newly-allocated IPs and ranges.
How to fix 550 5.7.708
- Request mitigation via Microsoft's delist portal for the IP.
- If you're on a shared IP, move to a dedicated one or a different provider.
Why this happens
Receivers score every sending IP and domain. A history of complaints, spam-trap hits, high bounce rates or a listing on a blocklist pushes that score down until mail is deferred or refused outright.
How to keep it from coming back
Warm up new domains and IPs gradually, send only to verified and relevant recipients, keep complaints near zero, and check your IPs and domains on blocklists regularly. Spread volume across mailboxes and domains instead of pushing one harder.
Should I retry a 550 5.7.708 error?
Not as it stands. A permanent error means the same message will be refused again until the cause is fixed on your side. Fix the cause first, then send a fresh message; if it keeps failing after that, check the full text of the bounce for the exact reason.
Got the full bounce message?
The text after the code names the exact reason, and the same code can mean different things at different receivers. Paste the whole message into the decoder - it runs in your browser and nothing is sent.
Open the bounce decoderRelated error codes
Seeing this again and again? That's usually a reputation or authentication problem we can trace and fix at the source.
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