Gmail 421 4.7.0: suspicious message, low reputation
421 4.7.0Message deferred as suspicious due to low reputationTemporary: the sender retriesFrom Gmail and Google Workspace
421-4.7.0 [203.0.113.60 15] Our system has detected that this message is suspicious due to the very low reputation of the sending domain. To best protect our users from spam, the message has been blocked. - gsmtp
What it means
Gmail returns this temporary 4.7.0 when a message looks suspicious and the sender has poor standing, but Gmail is not yet sure enough to reject it permanently. The text usually reads like the example and refers to the reputation of the sending IP address or domain. Because it starts with 4, your server keeps the message and tries again.
Treat it as an early warning. It sits between the 4.7.28 volume throttle and the permanent 5.7.1 reputation block. If the queue retries for days without success, the message eventually expires with a 4.4.7 delay bounce.
Likely causes
- A low or falling domain reputation in Postmaster Tools after a poorly targeted campaign.
- Mail sent from a recently registered domain with no positive engagement history.
- Inconsistent sending: big bursts followed by silence, which looks like a spam run.
- Content or links shared with known spam campaigns combined with a weak sender history.
How to fix it
- Let your MTA keep retrying with normal backoff; do not open many parallel connections to force mail through.
- Check domain and IP reputation in Postmaster Tools, and look at which streams (marketing versus transactional) were sent when it started.
- Separate transactional and marketing mail onto different subdomains or IPs so one does not harm the other.
- Reduce volume to engaged recipients until the deferrals fade.
Checks that apply
- Google/Yahoo Compliance Confirms authentication, PTR, TLS, and unsubscribe settings so reputation is the only open question.
- Blacklist Check Spots public listings that suggest a wider abuse problem behind the low reputation.
- MailFlow Monitor Watches whether a test message reaches Gmail or keeps being deferred.
FAQ
- Will my queued mail eventually get through?
- Often yes, if reputation recovers before your queue lifetime runs out (commonly five days). Otherwise the sender gets a delay expiry bounce.
- Is this different from 421 4.7.28?
- Yes. 4.7.28 is about a rate of unsolicited mail and throttles throughput; this 4.7.0 text is a per-message suspicion tied to reputation.