Defined SMTP Extensions
The non-required SMTP command set:
Service Ext EHLO Keyword Parameters Verb Added Behavior
------------- ------------ ---------- ---------- ------------------
Send SEND none SEND defined in RFC 821
Send or Mail SOML none SOML defined in RFC 821
Send and Mail SAML none SAML defined in RFC 821
Expand EXPN none EXPN defined in RFC 821
Help HELP none HELP defined in RFC 821
Turn TURN none TURN defined in RFC 821
Later additions, defined in other RFCs:
EHLO RFC1651 “SMTP Service Extensions”
8BITMIME RFC1652, “SMTP Service Extension for 8bit-MIME transport”
SIZE RFC1653, “SMTP Service Extension for Message Size Declaration”
X extensions (defined to be undefined)