Gmail delivery response

Gmail 421 4.7.0: Try again later, closing connection

Gmail uses 421 4.7.0 for several temporary conditions. The words after the code identify whether to check the connection, PTR, TLS, reputation, content, or a Google Workspace allowlist.

Problem description

A representative response is:

421 4.7.0 Try again later, closing connection.

Is this temporary or permanent?

Treat this as persistent transient until the complete provider response and retry behavior show otherwise.

Read the text after the code

Connection expired or Try again later: let the queue reconnect with backoff.
does not have a PTR record: correct reverse and forward DNS for the sending IP.
TLS required: enable TLS for that route.
low reputation or suspicious: stop unwanted traffic and investigate the named IP, domain, content, or links.
IP not in whitelist: review the recipient domain’s Workspace allowlist.

What to do

Save the complete response, timestamp, sending IP, and queue ID.
Keep normal queued retries with increasing delays.
Fix only the condition named after 4.7.0.
Send one controlled test after the correction.

MailFixIt scope

The short code alone does not prove a DNS problem. MailFixIt can check public DNS when the full text names PTR or another domain configuration issue, but it cannot reproduce Gmail reputation or content decisions.

Frequently asked questions

What does Gmail 421 4.7.0 mean?

Gmail temporarily deferred the SMTP connection. The remaining response text identifies the specific cause.

Can MailFixIt prove this entire bounce from public DNS?

No. The current checker can evaluate selected public DNS configuration, but it cannot recreate recipient state, credentials, reputation, message content, or a historical provider SMTP decision.

Related email diagnostics

SMTP 5.7.1: Delivery not authorizedSMTP 5.7.1 means delivery is not authorized; use the full response to identify a recipient restriction, relay permission, transport rule, or filtering policy. Gmail 550 5.7.1: Delivery not authorizedGmail 550 5.7.1 is a broad permanent rejection; match the exact response text to a policy, relay, reputation, header, rate-limit, or IPv6 problem before acting.

Primary sources: Gmail SMTP errors and codes, Google email sender guidelines.