SMTP session
One SMTP connection from the server greeting to QUIT, during which a client identifies itself, may authenticate and start TLS, and sends one or more messages.
What it means
A session opens when the server accepts the TCP connection and sends its 220 greeting, and ends when the client sends QUIT and the server answers 221, or when the connection drops. Within one session the client can run several mail transactions, one per message, starting each with MAIL FROM once the previous one has finished, or abandoning one with RSET.
Receivers judge the session as well as the message: the connecting IP and its reverse DNS, the EHLO name, whether TLS was used, and how many messages and recipients arrive per connection all feed filtering and rate limits. RFC 5321 expects a server to close a session on its own only after QUIT, after sending a 421 reply, or after a timeout.
Related terms
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 5321, section 3.1: Session Initiationrfc-editor.org
- RFC 5321, section 3.8: Terminating Sessions and Connectionsrfc-editor.org
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