550 5.1.1: Recipient address does not exist
550 5.1.1 means the receiving server looked up the address and found no mailbox for it. The failure is permanent, so sending the same message again will not help. Correct the address or remove it from your list.
- Bounce type
- Hard bounce (permanent)
- Usually caused on
- The recipient's side
- Terlido report label
- Invalid recipient
What the standard says
RFC 5321 defines reply code 550 as "mailbox unavailable": the mailbox was not found, cannot be accessed, or was refused for policy reasons. RFC 3463 adds the enhanced code 5.1.1. Class 5 is a permanent failure, subject 1 is addressing, and detail 1 is "Bad destination mailbox address". Read together, the domain answered but the part before the @ is not a mailbox it knows.
What the mailbox providers say
- Gmail (550 5.1.1): “The email account that you tried to reach does not exist...” Source
- Microsoft 365 / Outlook (5.1.1): “Bad destination mailbox address” Source
Common causes
- A typo in the address, such as a missing letter in the name or a swapped character.
- The person left the company and the mailbox was deleted. This is the most common cause on an old list.
- A guessed address. Name permutations like first.last@ or flast@ are wrong for many contacts, and the server tells you so with this code.
- A list that is months or years old, where roles changed and mailboxes were closed.
- A catch-all or alias that the recipient's administrator removed.
- A role or shared address that the company removed, such as a sales or info mailbox that no longer exists after a team change.
How to fix it
- Check the address for typos and compare it with the source, such as the contact's own site or profile.
- Remove the address from the list. The server has told you it will never accept mail there.
- Run the whole list through a format and role check before the next send, so obvious errors never reach a campaign.
- If you guessed addresses, stop guessing for that company and find the real format from a confirmed contact first.
- Keep the date you collected each address. Old rows go bad faster than new ones, so re-check the oldest part of the list first.
Is it a deliverability problem?
One or two of these on a large send is normal. A high share is a sender-side problem, because mailbox providers treat a high rate of unknown recipients as a sign of a bought or stale list. As a rule of thumb, aim to keep this under about 2% of sends. Above that, your sender reputation drops and campaigns can hit their bounce limit and pause. Keep the source of every address in your list. When one source produces many of these codes, you can drop that source instead of guessing. Also check the pattern: if the same company returns this code for several people, your guessed format for that company is wrong.
How Terlido handles it
When a bounce message for this code arrives in a connected mailbox, Terlido reads the status code. An enhanced code that starts with 5 is a hard bounce. In the campaign Reports tab this one is grouped as "Invalid recipient".
On a hard bounce Terlido adds the address to the workspace blocklist with the reason "hard bounce", so no campaign emails it again. The lead stops in that campaign as bounced, its lead score goes down by 15, and the bounce counts toward the campaign's bounce rate.
Once a campaign has at least 20 sends, it pauses itself when hard bounces divided by sends goes over the campaign's maximum bounce rate. The default is 5%. If the cause was on your side and you fixed it, you can remove the entry on the Blocklist page of your account settings and try again.
Check the domain behind the bounce
The free domain checker runs live SPF, DKIM, DMARC, MX and blocklist lookups and explains each result in plain English.
Free tools that help
- Email list format checkerReview CSV structure, empty addresses, and basic email syntax without contacting mail servers.
- Role-based email detectorFlag generic inbox prefixes in a pasted list.
- Bounce rate calculatorCalculate bounced messages as a share of attempted sends.
Related error codes
- 550 5.1.2: Recipient domain does not exist
- 553 5.1.3: Recipient address is not valid
- 550 5.1.10: Recipient not found
- 550 5.2.1: Mailbox disabled or not accepting mail