Permanent failure — do not retry
SMTP 550 5.4.1
recipient address rejected, access denied
SMTP 550 5.4.1 is Microsoft 365's rejection for an address it does not recognise or will not accept mail for. In practice it behaves like 5.1.1 — a hard bounce on a non-existent or disabled mailbox — and is the code you see most often when sending to Outlook and Exchange Online domains.
How it appears
550 5.4.1 Recipient address rejected: Access denied. AS(201806281)
550 5.4.1 [user@example.com]: Recipient address rejected: Access denied
What causes it
- The mailbox does not exist in the tenant, or was converted to a shared or disabled account.
- The domain is registered in Microsoft 365 but the specific user was never created.
- A directory-based edge block is refusing mail for unknown recipients in that tenant.
How to fix it
In order — try the first one first.
- Treat it as a hard bounce and remove the address.
- If you expected the address to work, confirm the exact spelling with the recipient — Microsoft tenants do not accept close matches.
- For a whole domain returning 5.4.1, the tenant is likely blocking unknown recipients wholesale, and no address list will get through until someone there allows you.
Common questions
- What does SMTP 550 5.4.1 mean?
- SMTP 550 5.4.1 is Microsoft 365's rejection for an address it does not recognise or will not accept mail for. In practice it behaves like 5.1.1 — a hard bounce on a non-existent or disabled mailbox — and is the code you see most often when sending to Outlook and Exchange Online domains.
- Should I retry a 550 5.4.1 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 5.4.1?
- Treat it as a hard bounce and remove the address.
Last reviewed 2026-09-11