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.
Should you remove the address?
Read the reply text before deciding
Remove it if the text says the account is inactive. Keep it if the text says the user is receiving mail too fast; that is a temporary condition on their side.
Hard bounce. Do not retry. It will fail every time.
How it appears
550 5.2.1 The email account that you tried to reach is disabled
550 5.2.1 <[email protected]>: 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.
Who sends it
Gmail and Google Workspace document both variants. Other servers use 5.2.1 for disabled or suspended mailboxes.
Gmail
Reply text The email account that you tried to reach is inactive.
The account has been disabled. Gmail links to its help page about disabled users.
Gmail
Reply text The user you are trying to contact is receiving email at a rate that prevents additional messages from being delivered.
This one is about the recipient's incoming volume, not your list. Gmail also sends it as a 450 4.2.1 deferral.
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.
- Is 550 5.2.1 a hard bounce or a soft bounce?
- 550 5.2.1 is a hard bounce. The receiving side has said the address can't receive mail, so a retry won't deliver it. Do not retry. It will fail every time.
- Should I remove the address after a 550 5.2.1 bounce?
- Remove it if the text says the account is inactive. Keep it if the text says the user is receiving mail too fast; that is a temporary condition on their side.
- Will verifying my list prevent 550 5.2.1?
- Yes. A mailbox check asks the recipient's server whether the address exists without sending anything, so addresses that would return this code are flagged before the send instead of bouncing against your domain.
Clean the list before the next send.
A bounce report only tells you about the addresses you already mailed. The rest of the list has the same kinds of dead mailboxes in it, and each one becomes a hard bounce recorded against your domain the moment you send.
- A real SMTP mailbox check on every row, before anything is sent
- Dead and mistyped addresses split out, so they never reach your sending tool
- Catch-all, disposable and role addresses flagged alongside
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Other 550 replies
- 550 5.1.1 — mailbox does not exist
- 550 5.7.1 — message refused by policy
- 550 5.4.1 — recipient address rejected, access denied
- 550 — mailbox unavailable
- 550 5.1.0 — address rejected, other address status
- 550 5.1.10 — recipient not found (Microsoft 365)
- 550 5.1.8 — bad outbound sender (Microsoft 365)
- 550 5.4.5 — daily sending limit exceeded (Gmail)
- 550 4.4.7 — message expired in the queue
- 550 5.7.25 — no PTR record for sending IP (Gmail)
- 550 5.7.26 — blocked, sender unauthenticated (Gmail)
- 550 5.7.27 — SPF authentication failed (Gmail)
- 550 5.7.28 — unusual rate of unsolicited mail (Gmail)
- 550 5.7.23 — SPF violation (Microsoft 365)
- 550 5.7.124 — sender not in allowed senders list (Microsoft 365)
- 550 5.7.509 — DMARC failed, policy reject (Microsoft 365)
- 550 5.7.606-649 — banned sending IP (Microsoft)
- 550 5.7.705 — tenant has exceeded threshold (Microsoft 365)
- 550 5.7.708 — traffic not accepted from this IP (Microsoft 365)
- 550 5.7.750 — blocked from sending from unregistered domains (Microsoft 365)
- 550 5.7.515 — authentication required for high-volume senders (Outlook.com)
- 550 5.7.1 S3140 — IP range on Outlook.com block list
- 550 5.5.0 — Mailbox unavailable (Outlook.com, Hotmail)
- 550 5.7.12 — Sender not authenticated by organization (Microsoft 365)
- 550 5.7.513 — Blocked by the recipient's own block list (Microsoft 365)
Sources
- Source: Google Workspace Admin Help: Gmail SMTP errors and codes
- Source: RFC 3463: Enhanced Mail System Status Codes
Provider wording is quoted only where the provider publishes it.
Last reviewed 2026-10-22