421 4.3.0: temporary system problem
Gmail closed the connection because of a passing problem on its own systems. The reply points at Google's side, and a retry should deliver the message.
- Gmail
- Provider
- Temporary (4xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 421 4.3.0
- Provider
- Gmail and Google Workspace
- Temporary or permanent
- TemporaryThe sending server keeps the message and tries again later.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
421 4.3.0 Temporary System Problem. Try again later.
What it means
A 421 reply means the receiving server is closing the connection and will not take mail on it for now. With 4.3.0 and these words, Gmail says the trouble is on its own systems. Your server should treat it like any other deferral: keep the message, wait, and retry. Replies like this are usually short lived and clear without anyone acting. If they last for hours, or appear for every message to Gmail, check the Google Workspace Status Dashboard and look in your own logs for a pattern, such as a single sending IP or one connection setting, before assuming the fault is Google's.
Common causes
- A temporary fault or overload on Google's mail servers.
- Maintenance or a partial outage on the Gmail side.
How to fix it
- 01Let your server retry on its normal schedule.
- 02If failures continue, check the Google Workspace Status Dashboard for a reported incident.
- 03Compare failures across your sending IPs and servers; if only one is affected, look at that machine's network and DNS.
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
Related codes
- 451 4.3.0Message temporarily rejected.Gmail turned your message away for now without giving a reason. It is a temporary failure, and your server should try it again later.
- 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.
- 5.3.0Receiving system problem, unspecified.The receiving server normally accepts mail, but a problem on that system itself, rather than with the mailbox or the message, stopped this delivery.
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