Simple Mail Transfer Protocol

smtp

Send mail using telnet

telnet localhost 25 Connect to the server
HELO 6bit.ch Greet the server.
MAIL FROM: [email protected] Set the FROM field
RCPT TO: [email protected] Set the TO field
DATA Enter message, starting with 'From: [email protected]' 'To: [email protected]' 'Subject: zzz', followed by message body and ending with '.'

Send mail using telnet with STARTTLS handshake

openssl s_client -debug -starttls smtp -crlf -ign_eof -connect 10.13.12.52:587