Extended Simple Mail Transfer Protocol (ESMTP)

Extension to SMTP that use TLS for encryption.

Commands

Same as SMTP, but instead of using the HELO command, ESMTP uses the EHLO command.

Examples

S: 220 smtp2.example.com ESMTP Postfix
C: EHLO bob.example.org
S: 250-smtp2.example.com Hello bob.example.org [192.0.2.201]
S: 250-SIZE 14680064
S: 250-PIPELINING
S: 250 HELP