4.4.2: connection dropped

What it means

With 4.4.2 the two servers did connect, but the transaction did not complete: the connection timed out, was reset, or was too poor to carry the message. RFC 3463 calls it useful only as a persistent temporary error, and the registry pairs it with reply code 421. The sending server retries, and a later attempt often succeeds. When it repeats for one destination, the receiving side may be closing connections on purpose, for example to limit how fast you send, and any reply text that arrived before the drop is worth reading.

Common causes

• A timeout during the transfer, often with large messages on a slow link.
• The receiving server closed the connection early because of load or rate limits.
• Network trouble, or a firewall or proxy that drops long connections.

How to fix it

1. 01Let the queue retry.
2. 02If it repeats for one domain, send to that domain more slowly.
3. 03If you run the sending server, check its logs for the step where the connection died (greeting, TLS, DATA).
4. 04Check the size of the affected messages; very large ones are more exposed to timeouts.

Sources

What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.

• RFC 3463, section 3.5: Network and Routing Statusrfc-editor.org
• IANA, SMTP Enhanced Status Codes registry (Enumerated Status Codes)iana.org