550 5.1.1: recipient 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.
- Fastmail
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 550 5.1.1
- Provider
- Fastmail
- 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 5.1.1 Recipient address rejected: User unknown in virtual mailbox table
What it means
When Fastmail itself returns this 550 5.1.1, there does not seem to be a user with that address on its system. Fastmail lists other wordings for the same problem: "Sorry, user address unknown", and "User unknown in local recipient table". The first thing to check is the spelling of the address. If it is right, Fastmail suggests reaching the person another way and telling them about the bounce, since it can mean their account is inactive or not receiving mail properly. The message will not be retried.
Common causes
- A typo in the address.
- The account was closed, or the address was removed or renamed.
- The address was never set up on the Fastmail account.
How to fix it
- 01Check the spelling of the address.
- 02Contact the recipient another way and tell them about the bounce.
- 03Remove the address from your lists if it stays undeliverable.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Why messages bounce back (Fastmail help center)fastmail.help
- Undelivered email (Fastmail help center)fastmail.help
Related codes
- 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.
- 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 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found.The address does not exist in the destination system, is mistyped, or is cached in Outlook with details that are no longer valid.
Further reading
All 4 Fastmail codesEvery code in the wikiPaste your own bounce