Common causes
- The account was deactivated by the user or the provider.
- The mailbox was suspended for abuse or unpaid fees.
- An employee mailbox was disabled after they left.
- The address is a forwarding stub that no longer points anywhere.
How to fix it
- Remove the address from your list.
- If it was a customer, look for a newer address in your records.
- Do not retry; the answer will not change.
- Check older parts of your list for the same domain.
How to prevent it Take the address off your list and verify the rest before the next send.
Frequently asked questions
Is this a hard bounce?
Yes. It is a permanent failure and should be suppressed.
Can verification find disabled mailboxes?
Often yes: many servers give the same answer during the check, and Mailcut then reports the address as Invalid.