421 4.7.0 error from Gmail: try again later
Gmail's 421 4.7.0 is a temporary refusal with several causes: low IP or domain reputation, suspicious links, a missing PTR record, required TLS. Read the text.
What 421 4.7.0 means
421 4.7.0 This message is suspicious due to the very low reputation of the sending IP address.A reputation deferral: Gmail doesn't trust the sending IP (another version names the domain). Other 4.7.0 texts point to a missing PTR record, a TLS requirement, flagged content or links, a recipient allowlist, or a dropped connection.
List problem or sender problem?
Depends on the text. Most versions are about you (reputation, reverse DNS, TLS, content), but a couple are about the connection or a policy on their side, like an expired connection or an allowlist. It's a temporary failure: the sending server retries on its own, but repeated deferrals are a warning.
How to fix 421 4.7.0
- Match the text: add a PTR record, turn on TLS, or clean up suspicious links and content.
- For the reputation versions, slow down and review Google's guidance on blocked messages.
- For "connection expired" or a plain "try again later", a retry usually goes through.
In SendingOS, 421 4.7.0 shows on the conversation with its reason and code, so a problem on their side never gets mistaken for one on yours.
Not sure whether a spike in bounces is the list or the domain? Read High email bounce rate? Burned domain or bad list.
Related codes
Sources: Google: Gmail SMTP errors and codes · RFC 3463