What the receiver is telling you

The part after the @ does not resolve — no MX record, no A record, or the domain itself is not registered. Nobody at that domain is receiving anything. In practice it is a company that shut down or rebranded, a domain that expired, or a typo in the domain (gmial.com, outlok.com). It cannot succeed on retry because there is no server to retry against.

What a hard bounce means for your reputation

Receivers count hard bounces. Gmail and Microsoft both treat a sender whose mail is addressed to people who do not exist as a sender who did not get those addresses from the people themselves, which is the definition of unsolicited. The working threshold is two percent of a send: under that is noise, above it starts to cost domain reputation, and above five percent a fresh domain can be throttled after a single campaign. The fix is upstream — verify before sending — not downstream.

What to do

1. Remove the address. If several addresses share the domain, remove them all — the domain is gone, not the person.
2. Run the list through a cleaner that checks MX per domain before the next send; dead domains are cheap to catch.
3. If the domain is a typo of a real one, correct it rather than deleting — j.smith@gmial.com is a real lead with a broken domain.
4. For a domain you expected to work, look it up: the company may have moved to a new domain and left the old one to lapse.

don't Do not keep the address in case the domain comes back. Expired domains are re-registered by other people and become spam traps.

Decode the whole bounce

Paste the complete failure notice — every code and the receiver's wording — and get each part explained together.

Common questions