421 4.7.0: sending IP not on the domain's allowlist
The Google Workspace domain you are writing to only accepts mail from listed IP addresses, and the IP you send from is not one of them.
- Gmail
- Provider
- Temporary (4xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 421 4.7.0
- Provider
- Gmail and Google Workspace
- Temporary or permanent
- TemporaryThe sending server keeps the message and tries again later.
- Who has to act
- The recipient's side. Their mail admin has to change something; you can tell them.
- What the server says
421 4.7.0 IP not in whitelist for RCPT domain, closing connection.
What it means
Some Workspace admins restrict their domain so that only certain IP addresses may deliver to it, typically when inbound mail is meant to arrive through a filtering gateway or a partner's servers. Your sending IP is not on that list, so Gmail closes the connection with this reply. Google's sender guidelines describe the same code: the sending server's IP is not on the allowed list for the recipient's domain. The reply is temporary in form, but retries fail the same way until the recipient's admin changes the setting or you deliver through an IP they accept. Nothing in your own DNS or reputation changes it.
Common causes
- The recipient's admin limits inbound mail to listed IP addresses, often those of a security gateway in front of Workspace.
- You now send from a new or different IP than the one the recipient's organization allowed.
How to fix it
- 01Contact the recipient through another channel and ask their admin to add your sending IP, or to tell you which route to use.
- 02Check that you deliver to the hosts in the recipient domain's MX records, and not straight to Google through a fixed route.
- 03If you changed sending providers or IP addresses, give the recipient's admin the new ones.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Gmail SMTP errors and codes (Google Workspace Admin Help)knowledge.workspace.google.com
- Email sender guidelines (Gmail Help)support.google.com
Related codes
- 421Service not available.The receiving server is closing the connection and will not take mail right now. The reply is temporary, so the sending server keeps the message and tries again later.
- 5.7.0Security or policy refusal, unspecified.The message or session was refused for a security or policy reason that the server did not describe more precisely, or chose not to reveal.
Further reading
All 108 Gmail codesEvery code in the wikiPaste your own bounce