RSET
The SMTP command that abandons the current mail transaction, discarding sender, recipients and data, without closing the connection.
What it means
RSET clears everything given since the last MAIL FROM and returns the session to the state it was in just after EHLO. The server must answer 250 and must not close the connection, which makes RSET the usual way to start over or to move to a new message on the same connection. A later EHLO resets the transaction too, so RSET followed by EHLO is redundant.
Sending software uses it when a transaction goes wrong half way, for example when every recipient was refused. RFC 1870 tells clients to send RSET or QUIT after a SIZE refusal, and Google's SMTP relay service asks clients that reach its 100-recipient limit to start another transaction with a new connection or RSET.
Related terms
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 5321, section 4.1.1.5: RESET (RSET)rfc-editor.org
- RFC 1870: SMTP Service Extension for Message Size Declarationrfc-editor.org
- Google Workspace Admin Help: Route outgoing SMTP relay messages through Googleknowledge.workspace.google.com
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