Common causes
- A typo in the domain name.
- The domain expired or was never registered.
- A company closed and let its domain lapse.
- The domain has no mail records and no address record.
How to fix it
- Check the spelling of the domain and correct obvious typos.
- Look the domain up (an MX lookup shows whether it can receive mail).
- Remove the address if the domain is gone.
- Fix the sign-up form so bad domains are caught on entry.
How to prevent it Take the address off your list and verify the rest before the next send.
Frequently asked questions
How is it different from 5.1.1?
5.1.1 means the domain works but the mailbox does not exist. 5.1.2 means the domain itself cannot receive mail.
What does Mailcut do?
Addresses at domains with no mail servers are reported as Invalid before any mailbox check is attempted.