Microsoft (Outlook.com and Microsoft 365) · permanent error
550 5.5.0: outlook.com or Hotmail address not found
Microsoft found no mailbox with this address at hotmail.com or outlook.com; it works like 5.1.10 for consumer addresses.
- Microsoft
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 550 5.5.0
- 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 the server says
550 5.5.0 Requested action not taken: mailbox unavailable
What it means
Microsoft lists 550 5.5.0 for mail to an @hotmail.com or @outlook.com address that is not found by SMTP address lookup. In effect, Microsoft's consumer service is saying the mailbox does not exist, and Microsoft points to its 5.1.10 guidance for it. The address may be mistyped, or the account may have been closed. Since the mailbox is not there, resending will not help; remove the address from your lists if it keeps bouncing.
Common causes
- The Outlook.com or Hotmail address is misspelled.
- The account no longer exists or never existed.
How to fix it
- 01Check the spelling, including the domain (outlook.com or hotmail.com).
- 02Confirm the address with the recipient by another channel.
- 03If you send to lists, remove the address so repeated bounces do not hurt your reputation with Outlook.com.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Email nondelivery reports and SMTP errors in Exchange Onlinelearn.microsoft.com
Related codes
- 550 5.1.10Recipient not found by SMTP address lookup.The recipient's domain is served by Exchange Online, but no recipient there has the address you sent to.
- 550 5.1.1Recipient address not found.The address does not exist in the destination system, is mistyped, or is cached in Outlook with details that are no longer valid.
- 550Mailbox unavailable.The receiving server permanently refused the message for this recipient: the mailbox does not exist, cannot be reached, or the server rejected the message by policy.
Further reading
All 111 Microsoft codesEvery code in the wikiPaste your own bounce