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550 5.1.1 recipient address rejected

What the 550 5.1.1 bounce means, why mail to a nonexistent or mistyped address is rejected, and what to do about it as a sender or as the domain owner.

What 550 5.1.1 means

A 550 5.1.1 bounce means the recipient's mail server does not have a mailbox for the address you wrote to. The basic code 550 is a permanent failure. In the enhanced status code (RFC 3463), subject 1 is addressing and 5.1.1 is "bad destination mailbox address": the domain is fine, the part before the @ is not.

Gmail's version reads:

550-5.1.1 The email account that you tried to reach does not exist. Please try
550-5.1.1 double-checking the recipient's email address for typos or
550-5.1.1 unnecessary spaces.

Other servers say "User unknown", "Recipient address rejected: User unknown in virtual mailbox table" (Postfix) or "RecipientNotFound" (Microsoft 365). The meaning is the same.

Common causes

  • A typo in the local part: jhon@ instead of john@, a stray space or a missing letter.
  • The person left and their mailbox was deleted.
  • An old list. Addresses go stale; mailing them repeatedly hurts your reputation.
  • A misconfigured receiving server: the domain moved to a new provider but the mailbox was not created there, or the MX records still point at the old one.
  • Aliases or groups that were removed or never set up on the new system.
  • Backscatter: if you received a 5.1.1 for a message you never sent, someone forged your address. Strict SPF and DMARC make that less likely to be accepted elsewhere.

What to do as a sender

  1. Check the address for typos and confirm it with the recipient another way.
  2. Don't retry. A 550 is final, and sending to the same address again counts against you.
  3. Remove hard bounces from lists right away. Email services do this automatically; if you send yourself, process bounces and suppress those addresses.
  4. Use confirmed opt-in for signups so typos never reach your list.

What to do as the domain owner

If people tell you they get 5.1.1 for an address that should exist:

  1. Confirm the mailbox or alias exists in your provider's admin panel, including the exact spelling.
  2. Check where mail goes. The domain's MX must point at the provider that holds the mailbox:
dig example.com MX +short
  1. After a migration, look for leftover MX records from the old provider and wait out the TTL. The DNS Propagation Checker shows whether resolvers still return old servers.
  2. On Postfix, test the lookup that rejects the address:
postmap -q john@example.com hash:/etc/postfix/virtual
  1. Catch-all: accepting every address avoids 5.1.1 but attracts spam. Prefer explicit aliases.

To read the bounce itself (which server rejected it, and when), paste it into the Email Header Analyzer.

Check the recipient domain's MX records with the DNS Lookup, or its whole email setup with the Email Checker.