What the receiver is telling you

Gmail's rate and reputation block. The 4.7.28 form is a throttle: Gmail is deferring your mail because the volume or the spam-report rate crossed a line, and it will accept it later if you slow down. The 5.7.28 form is the same signal after it stopped being temporary: the IP or domain has been classified as a source of unsolicited mail and is blocked outright. On Google Workspace the IP is Google's own, which means the block is keyed on your domain's behaviour, and the fix is on the domain.

Why a policy block must not be treated as a bad address

Sending tools file every 5xx under "bounced", and the natural reflex is to scrub the address. For a policy block that is exactly wrong. The recipient exists and would have received the mail; the receiver refused it because of your domain, IP, authentication or content. Scrubbing throws away a lead and leaves the cause in place, so the next send produces the same block against the next thousand addresses. The right response is to stop sending from the affected domain, find what the receiver named, fix it, and resume at low volume.

What to do

1. Stop sending to Gmail from the affected domain immediately. Continuing turns 4.7.28 into 5.7.28.
2. Open Google Postmaster Tools for the domain and check spam rate and domain reputation. Anything over 0.3% spam rate is the cause.
3. Cut per-inbox volume to under 20 a day, verify the list, and remove every address that has never engaged.
4. If the block is 5.7.28, plan to rotate the domain out. Recovery from a hard reputation block is slow and often incomplete.

don't Do not increase the number of inboxes on the same domain to get around a throttle. That is exactly the pattern the rule detects.

Decode the whole bounce

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

Common questions