The SMTP ( Simpel Mail Transfer Protocol ) protocol uses port number 25.

Commands :

helo domain       - connection check between smtp servers
mail from:<adres> - email adres of sender
rcpt to:<adres>   - email adres of recipient
data message      - the email message
rset              - abort and reset current mail transmission
vrfy string       - confirm that string is a user name
help [command]    - list of avaible commands on server
quit              - close and quit transmission