Extended SMTP
Extended SMTP
Extended SMTP (ESMTP), sometimes referred to as Enhanced SMTP,is a definition of protocol extensions to the Simple Mail Transfer Protocol standard.
The extension format was defined in IETF publication RFC 1869 (1995) which established a general structure for all existing and future extensions.
ESMTP defines consistent and manageable means by which ESMTP clients and servers can be identified and servers can indicate supported extensions.
Extensions
The main identification feature is for ESMTP clients to open a transmission with the command EHLO (Extended HELLO), rather than HELO.
Some relatively common keywords (not all of them corresponding to commands) used today are:
