What is the basic SMTP protocol for sending mail?
RFC 2821 (http://www.faqs.org/rfcs/rfc2821.html) defines the SMTP protocol. To send a message you would normally open up port 25 on your mail server and send the following information:
HELO sending host MAIL FROM: sender email RCPT TO: recipient email DATA ... the email message... ... any number of lines ... . QUIT
Between the DATA line and the . (period) line is the message. The period is alone on the line following the end of the message.