550 5.4.1 error (Exchange Online): Recipient address rejected - the mailbox doesn't exist
The recipient domain uses Microsoft 365 with directory-based edge blocking, and no mailbox matches this address. In practice it's a bad address.
How to fix 550 5.4.1
- Remove or correct the address; it will never deliver.
- Verify addresses before sending - frequent hits like this raise your bounce rate.
Why this happens
The receiving server looked for the mailbox and couldn't find one it will accept. Typos, people who left a company, and lists that were scraped or are years old are the usual sources.
How to keep it from coming back
Verify addresses before you send and remove hard bounces immediately. Keep your bounce rate under about 2%; a list that produces many of these damages the reputation of the domain you send from.
Should I retry a 550 5.4.1 error?
No. This is a permanent failure for that address, so retrying only adds another bounce to your count. Remove the address from your list, or correct it if it's a typo.
Got the full bounce message?
The text after the code names the exact reason, and the same code can mean different things at different receivers. Paste the whole message into the decoder - it runs in your browser and nothing is sent.
Open the bounce decoderRelated error codes
Seeing this again and again? That's usually a reputation or authentication problem we can trace and fix at the source.
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