451 4.4.2: connection timed out

What it means

SMTP servers wait only so long between the steps of a conversation. If your server goes quiet in the middle, while sending the message body for example, Gmail gives up, sends this temporary reply and closes the connection. Nothing is delivered from that attempt, but because the code is temporary the sending server keeps the message and tries again. An occasional timeout is normal on the internet. Frequent ones point to a slow or overloaded sending server, a network path that loses packets, a firewall or antivirus product that inspects SMTP traffic, or a very large message on a slow link.

Common causes

• The sending server is overloaded and stalls during the SMTP conversation.
• Packet loss or a slow network path between your server and Google.
• A firewall, proxy or security product that holds SMTP traffic while it inspects it.
• A very large message sent over a slow uplink.

How to fix it

1. 01Let the retry run; a single timeout is rarely a problem.
2. 02If timeouts repeat, check the sending server's load and its network path to Google, for example with a traceroute.
3. 03Turn off SMTP inspection in any firewall or antivirus between your server and the internet, then test again.
4. 04For large messages, share attachments as links instead.

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