What the receiver is telling you

The address is real but the mailbox is closed. On Gmail that means the account was suspended or the Workspace user was deleted with the address kept as a placeholder. On Exchange it often means the mailbox is a shared or resource mailbox that refuses external mail, or the user is on litigation hold with delivery disabled. Either way, nobody reads what you send there, and a disabled Gmail account that later gets purged becomes a 5.1.1.

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. A disabled mailbox almost never comes back into use.
2. If the domain is a client's own Workspace and the user should exist, the admin needs to reinstate the account; the sender cannot fix it.
3. If you see it across many addresses at one company, they have restricted external mail for that group — move on.

don't Do not retry for weeks hoping the account is reactivated. Retries to disabled accounts are counted the same as retries to unknown ones.

Decode the whole bounce

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

Common questions