Microsoft (Outlook.com and Microsoft 365) · permanent error
550 [DY-002]: outlook.com block for a likely compromised sender
Outlook.com rejected the mail because the sending server or computer appears to be compromised or infected.
- Microsoft
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 550 [DY-002]
- 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
With DY-002, Outlook.com says the likely cause is a compromised or virus-infected server or personal computer, and it refuses the mail for policy reasons. If you did not intend to send mail from the IP, treat it as a security incident: find the infected machine, clean it, and stop devices that should not send mail from connecting directly to outside mail servers.
Common causes
- Malware on a computer or server is sending mail from your IP.
- A compromised mail account or web application is being used to send spam.
How to fix it
- 01Scan the machines behind the IP for malware and clean them.
- 02Block outbound port 25 from devices that should not send mail directly.
- 03Change passwords on mail accounts and applications that could have been abused.
- 04When the source is gone, submit the Outlook.com sender support form for the IP.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Outlook.com Postmaster: Troubleshooting (SMTP error codes)substrate.office.com
Related codes
- 550 [SC-003]Outlook.com block for an open proxy or relay.Outlook.com rejected the mail because the sending IP appears to be an open proxy or open relay.
- 550 [DY-001]Outlook.com refuses dynamic IP addresses.Outlook.com rejected the mail because the sending IP is dynamic address space, which it generally does not accept mail from.
550 at other providers
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
Further reading
All 111 Microsoft codesEvery code in the wikiPaste your own bounce