The Internet protocol used in the transfer of e-mail is SMTP, or Simple Mail Transfer Protocol. SMTP is usually accessed on port 25 of your Internet provider's SMTP server. If you manually telnet to port 25 of an SMTP server, an SMTP session is initialized. In such a session, the following commands can be used:

• HELO <hostname>
  Introduce yourself.
• EHLO <hostname>
  Introduce yourself and request extended SMTP mode.
• MAIL FROM: <sender>
  Specifies the sender.
• RCPT TO: <recipient>
  Specifies the recipient. Can be used any number of times.
• DATA
  Following text is collected as the e-mail message. End message with a period on a line by itself.
• RSET
  Resets the system. Once reset, a new sender can be specified.
• NOOP
  Do nothing.
• QUIT
  Exit sendmail (SMTP)
• HELP
  Gives command info. If used alone, displays commands implemented on specific system. If used as HELP <command>, specific information on that command is given.
• VRFY <recipient>
  Verify an address. To view aliases, use EXPN instead.
• EXPN <recipient>
  Expands an address. Same as VRFY, but includes aliases and mailing lists.
• VERB
  Goes into verbose mode. This sends responses that are not RFC821 standard (not accepted officially by Internet protocol standards). They are recognized by humans and other sendmail implementations, however.

220 mailhub.korg.net ESMTP (Sendmail 8.7.4/8.6.12 ready at Mon, 1 Jul
1996 06:24:36 -0400 (EDT)
helo data.korg.net
250 mailhub.korg.net Hello data.korg.net [127.0.0.1], pleased to meet you
mail from: johnr@data.korg.net
250 johnr@data.korg.net... Sender ok
rcpt to: maryk@avon.com
250 Recipient ok
data
354 Enter mail, end with "." on a line by itself
From: Johnr@data.korg.net (John Rinaldo)
To: maryk@avon.com (Mary Kay)
Subject: New cosmetics product

Please send me any info about your new cosmetics line.  Thanks!
.
250 AAA25285 Message accepted for delivery
221 mailhub.korg.net closing connection