SMTP timeout
How long each side of an SMTP session waits for the other; RFC 5321 sets minimums per command, such as five minutes for the greeting and ten for the reply after the data.
What it means
RFC 5321 requires clients to time each command separately rather than the whole transaction, with these minimums: 5 minutes for the 220 greeting, for MAIL and for each RCPT; 2 minutes for the 354 reply to DATA; 3 minutes for each block of data sent; and 10 minutes for the reply after the final dot. A server should wait at least 5 minutes for the client's next command.
The long final wait exists because giving up there is costly: if the client disconnects while the server is still processing a message it has in fact accepted, the client retries and the recipient receives a duplicate. Timeouts in logs point to network trouble, an overloaded receiver or deliberate slowing such as tarpitting.
Related terms
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 5321, section 4.5.3.2: Timeoutsrfc-editor.org
- RFC 5321, section 6.1: Reliable Delivery and Replies by Emailrfc-editor.org
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