550 5.1.1: recipient 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The address does not exist in the destination system, is mistyped, or is cached in Outlook with details that are no longer valid.
- Microsoft
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 550 5.1.1
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- Either side, depending on the cause. Start with the checks below that are yours.
- What the server says
550 5.1.1 Bad destination mailbox address
What it means
Microsoft calls a wrong email address the most common cause of 5.1.x errors. 5.1.1 means the receiving system could not find the recipient: usually a typing error, or an address that was valid once and has since been changed or removed. Inside an organization it can also come from a stale Outlook Auto-Complete entry after a mailbox move, an invalid legacy distinguished name (the ExRecipNotFound and IMCEAEX reports), or a forwarding rule that sends a copy to an address that no longer exists. Resending the same message unchanged fails again. If you never sent the original, the report may be backscatter from a spammer forging your address.
Common causes
- The address is misspelled.
- The mailbox was removed or renamed.
- Outlook's Auto-Complete entry points to an old internal address after the mailbox moved.
- The recipient has a forwarding rule to an address that no longer exists.
- The recipient domain's MX record points to an old mail server.
How to fix it
- 01Check the spelling of the address and write a new message, rather than resending the failed one.
- 02Delete the recipient from your Auto-Complete list and type the address in full.
- 03If the address in the report differs from the one you used, ask the recipient to fix or remove their forwarding rule.
- 04If you did not send the original message and your Sent Items show nothing unusual, the report is backscatter and can be ignored.
- 05Admins: for an IMCEAEX address, add the old legacyExchangeDN as an X500 proxy address on the mailbox, and check that the domain has a single correct MX record.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Fix non-delivery report (NDR) error code 550 5.1.1 through 550 5.1.20 in Exchange Onlinelearn.microsoft.com
- "550 5.1.1 RESOLVER.ADR.ExRecipNotFound" when sending emails by using Outlook in Microsoft 365learn.microsoft.com
- IMCEAEX non-delivery report when you send email messages to an internal user in Microsoft 365learn.microsoft.com
- 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 5.4.1Recipient rejected by Directory-Based Edge Blocking.Microsoft 365 rejected the message at its edge because the recipient address does not exist in the destination tenant.
- 5.1.1Mailbox does not exist.The recipient's domain accepts mail, but the mailbox named before the @ does not exist there, so the message was refused and will not be delivered.
5.1.1 at other providers
- 550 5.1.1Recipient address does not exist.There is no Gmail or Google Workspace account at the address you wrote to, so Gmail rejected the message permanently.
- 550 5.1.1Recipient address does not exist.Fastmail could find no user with the address you wrote to. Check the spelling; if it is right, the account may be inactive or closed.
Further reading
All 111 Microsoft codesEvery code in the wikiPaste your own bounce