SMTP transaction
The part of an SMTP session that delivers one message: a MAIL FROM command, one RCPT TO per recipient, then DATA and the message itself.
What it means
RFC 5321 calls it a mail transaction. MAIL FROM starts it and gives the envelope sender; each RCPT TO names a recipient and is accepted or refused on its own; the reply after the message data ends it. RSET abandons a transaction without closing the connection.
Because each recipient gets its own reply, one transaction can partly succeed: two recipients accepted, a third refused with 550 5.1.1. The final reply after the data then applies to every recipient that was accepted. Receivers also set limits per transaction: Gmail answers too many recipients with 452 4.5.3, and several recipient domains in one transaction with 451 4.3.0, both temporary.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 5321, section 3.3: Mail Transactionsrfc-editor.org
- Google Workspace Admin Help: Gmail SMTP errors and codesknowledge.workspace.google.com
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