Microsoft 365 550 5.7.708: “Access denied, traffic not accepted from this IP”

Short answer: Exchange Online refused to send your mail because the outgoing IP it would use is treated as low reputation. This mostly hits new or trial Microsoft 365 tenants. Fix: make sure the mailbox has an Exchange Online licence and your domain is verified, then ask Microsoft support for an exception. Nothing in your DNS causes it.

The bounce looks like this
550 5.7.708 Service unavailable. Access denied, traffic not accepted from this IP.

What it means

The bounce comes from your own Microsoft 365 tenant, not from the recipient. Exchange Online keeps new and trial tenants on a separate, low-reputation sending pool and can stop their outbound mail. It can also happen after the tenant sent suspicious mail, for example from a compromised account.

How to fix it

  1. Check that the sending mailbox has an Exchange Online licence assigned and that your custom domain is verified in the Microsoft 365 admin center (trial tenants are the usual case).
  2. Look for compromise: unknown inbox rules, unexpected forwarding or a spike in sent mail. Reset passwords and turn on MFA before anything else.
  3. Open a service request in the Microsoft 365 admin center. Include the full bounce, the sending mailbox and how the mail was sent (Outlook, Outlook on the web, a connector or an app), and ask for the IP exception.
  4. If the mail is sent by a third-party app through your tenant, that app's provider may need to raise it with Microsoft as well.
  5. Use the time to get SPF, DKIM and DMARC right for the domain (check it below), so mail lands in the inbox once Microsoft lifts the block.

Check your domain now

After the fix, send a test email to see SPF, DKIM and DMARC pass on a real message, then keep an eye on it: free DMARC monitoring shows every service that sends mail as your domain and which ones fail, in plain English.

Rather not touch DNS? I set up SPF, DKIM and DMARC without breaking your other senders, with a before/after report.

Get it fixed on Fiverr

Prefer to do it yourself? Get the step-by-step Fix Kit ($15) – 28-page guide, checklist, 20+ providers.

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