SMTP and the Message Envelope

1. Client connects to server's SMTP port (25).
2. Server: 220 staff.uiuc.edu ESMTP Sendmail 8.10.0/8.10.0 ready; Mon, 13 Mar 2000 14:54:08 -0600
3. Client: helo students.uiuc.edu
4. Server: 250 staff.uiuc.edu Hello root@students.uiuc.edu [128.174.5.62], pleased to meet you
5. Client: mail from: johndoe@students.uiuc.edu
6. Server: 250 2.1.0 johndoe@students.uiuc.edu... Sender ok
7. Client: rcpt to: jsmith@staff.uiuc.edu
8. Server: 250 2.1.5 jsmith@staff.uiuc.edu... Recipient ok
9. Client: data
10. Server: 354 Enter mail, end with "." on a line by itself
11. Client:

    Received: (from johndoe@localhost)
            by students.uiuc.edu (8.9.3/8.9.3) id LAA05394;
            Mon, 5 Jul 1999 23:46:18 -0500
    Date: Mon, 5 Jul 1999 23:46:18 -0500
    From: John Doe <johndoe@students.uiuc.edu>
    To: John Smith <jsmith@staff.uiuc.edu>
    Message-Id: <199907052346.LAA05394@students.uiuc.edu>
    Subject: This is a subject header.
    
    This is the message body.  It is seperated from the headers by a blank
    line.
    
    The message body can span multiple lines.
    
    .
    

12. Server: 250 2.0.0 e2DKuDw34528 Message accepted for delivery
13. Client: quit
14. Server: 221 2.0.0 staff.uiuc.edu closing connection

The sender and recipient addresses used in the SMTP transaction are called the Message Envelope. Note that these addresses do not need to have any similarity to the addresses in the message headers!