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Microsoft (Outlook.com and Microsoft 365) · permanent error

550 [SC-004]: outlook.com block after complaints

Outlook.com placed a block on the sending IP because it received complaints about mail coming from it.

Microsoft
Provider
Permanent (5xx)
Class
Sources checked
By , email deliverability consultant
Author

At a glance

Code
550 [SC-004]
Temporary or permanent
PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
Who has to act
The sender. The fix is on the sending side: your domain, your server or your list.

What it means

SC-004 is a block on the IP itself, placed because Outlook.com received complaints about mail from it. Microsoft's own advice in the code's explanation is to enroll in the Junk Email Reporting Program (JMRP), a free program that sends you the messages users mark as junk so you can remove those recipients from your list. Reducing complaints is the lasting fix, and a review request makes sense once you have done it.

Common causes

  • Outlook.com users marked mail from the IP as junk at a high rate.
  • The mailing went to recipients who did not ask for it or no longer want it.

How to fix it

  1. 01Enroll the IP in JMRP and suppress every address that reports your mail.
  2. 02Clean the list: remove inactive and unconfirmed addresses.
  3. 03Check complaint data for the IP in SNDS.
  4. 04Submit the Outlook.com sender support form once complaint rates are down.

Sources

What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.

  1. 550 [SC-001]Outlook.com policy block for content or reputation.Outlook.com rejected the mail for policy reasons tied to spam-like content or to the reputation of the sending IP or domain.MicrosoftPermanent

550 at other providers

  1. 550Refused for a header or address problem.Yahoo or AOL refused the message for a policy reason tied to its headers, its addresses or the sending domain's DNS. Yahoo lists these as other policy errors, sent as 550 or 554.YahooPermanent
  2. 550Not an Xfinity customer.The address you sent to does not belong to an Xfinity customer. The failure is permanent, and Xfinity asks bulk mailers to treat it as an unsubscribe.ComcastPermanent
  3. 550Too many invalid recipients.Xfinity refused the whole message because too many of its recipients were invalid, so nobody received it. Clean the recipient list and send it again.ComcastPermanent
  4. 550Sender domain has no A or MX record.Xfinity refused the message because the domain you send from has neither an A record nor an MX record in DNS. Add one and send again.ComcastPermanent
  5. 550Account not available.The Xfinity account you wrote to is currently not available. Xfinity sends this as a 550, so the message has failed, though the account itself may come back.ComcastPermanent
  6. 550Permanent reject under an exceptional blocklist.GMX permanently refused mail from your system because it is on one of the blocklists GMX uses in exceptional situations. The message comes back and is not retried.GMX, WEB.DEPermanent

Further reading

All 111 Microsoft codesEvery code in the wikiPaste your own bounce

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