Permanent failure — do not retry
SMTP 550 5.2.1
mailbox disabled, not accepting messages
SMTP 550 5.2.1 means the mailbox exists but has been disabled and will not accept mail. It is a permanent failure and a hard bounce. The usual cause is an account deactivated when someone left an organisation, with the address retained rather than deleted.
How it appears
550 5.2.1 The email account that you tried to reach is disabled
550 5.2.1 <user@example.com>: Recipient address rejected: mailbox disabled
550 5.2.1 Mailbox unavailable
What causes it
- The account was deactivated when the person left, but the address still exists in the directory.
- An administrator has suspended the mailbox.
- The address is a legacy alias pointing at a mailbox that no longer accepts mail.
How to fix it
In order — try the first one first.
- Remove the address. It is a hard bounce and it will not start working again.
- If it is a contact you need, find a current colleague rather than retrying — the person behind this address has almost certainly left.
- A cluster of 5.2.1 results from one company usually means a round of departures, and the rest of that company's contacts are worth re-verifying.
Common questions
- What does SMTP 550 5.2.1 mean?
- SMTP 550 5.2.1 means the mailbox exists but has been disabled and will not accept mail. It is a permanent failure and a hard bounce. The usual cause is an account deactivated when someone left an organisation, with the address retained rather than deleted.
- Should I retry a 550 5.2.1 error?
- No. 550 is a permanent failure, so the message will never be delivered no matter how many times you try. Remove the address — repeated sends to permanent failures are one of the main signals mailbox providers use to throttle a sender.
- How do I fix SMTP 550 5.2.1?
- Remove the address. It is a hard bounce and it will not start working again.
Last reviewed 2026-09-11