Documentation
550 5.1.1: the recipient address does not exist.
The receiving server looked for a mailbox with this name and found none.
What it means
A 5.1.1 reply is a permanent failure. The receiving server accepted the connection and then said that nothing is at that address, using words like "user unknown", "no such user", "recipient not found" or "mailbox unavailable". Codes 5.1.0 and 5.1.6 mean much the same thing.
Typical codes and wording
550 5.1.1, 5.1.0, 5.1.6 ("user unknown", "no such user", "mailbox unavailable")
Common causes
- A typo in the address, most often in the domain part (gmial.com) or a missing letter.
- The person left, or the mailbox was closed or deleted.
- The address came from an old, bought or scraped list, or was made up in a sign-up form.
- A forwarding rule on the recipient's side points at an address that no longer exists.
What to do
- Do not retry. Repeated sends to a dead address damage your sender reputation.
- Check the address for typos. If people type their own address, ask them to confirm it or show a hint when the domain looks misspelled.
- Remove the address from your list, or fix it and send once to the corrected address.
- If many bounces of this kind come from one signup form, add a confirmation step so only working addresses enter your list.
What Mailtruss shows
The message's status is Bounced, titled "Recipient address does not exist", with the receiving server's own words underneath. The address is added to your suppression list, so later sends to it are skipped until you remove it.
Is it safe to retry?
No. A retry will fail the same way.