550 5.1.1 User unknown / recipient address rejected
The most common bounce there is: the mailbox does not exist. The server owns the domain, looked for the local part, and found nothing. It is permanent and about the address, not about you.
What the server replies
550 5.1.1 <anna.keller@example.com>: Recipient address rejected: User unknown in virtual mailbox table
- Sent by
- Any mail server
- Type
- PermanentRetry fails
- About
- Recipient problems
- Enhanced code
- 5.1.1
Who sends it
Every mail server. Postfix says "User unknown in virtual mailbox table" or "in local recipient table" depending on how the domain is hosted; Exim says "Unrouteable address" or "No Such User Here"; Exchange says "RESOLVER.ADR.RecipientNotFound"; Gmail says "The email account that you tried to reach does not exist".
Why it happens
- A typo, including an extra dot or a dropped letter.
- The person left and the mailbox was deleted.
- An old list with addresses that have long since been removed.
- The domain recently moved to a new provider and the mailbox was not recreated there.
How to fix it
Confirm the address
Ask the person or check a recent message from them. For a business, the website's contact page is usually accurate.
Stop sending to it
One 5.1.1 is enough to suppress an address. Receivers measure the share of unknown users in your traffic and treat a high share as a sign of a bought list.
Admin: check the move
If the domain just changed providers, make sure every mailbox and alias was recreated and that the MX record points at the new host and not the old one.
Check it yourself
These free tools show the records and connections behind this code for your own domain or server.
Related codes
- 550 5.1.1 The email account that you tried to reach does not existThere is no mailbox at that address on Gmail or on the Workspace domain.
- 550 5.4.1 Recipient address rejected: Access deniedExchange Online looked the recipient up in the tenant's directory and did not find it, so it refused the address at RCPT TO.
- 554 delivery error: dd This user doesn't have a yahoo.com accountThe recipient address does not exist at Yahoo.
- 450 4.1.1 Recipient address rejected: unverified address / mailbox unavailableThe server could not confirm the recipient exists right now and is asking you to try again.
Sources
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Other free tools
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- Email header analyzerPaste raw headers to see every hop, where the delay was, and whether SPF, DKIM and DMARC passed.
- Email address validatorCheck whether an address is well formed, whether its domain accepts mail, and whether it is disposable or a role account.