SMTP looks exactly like this

$ telnet/port=25 arizona.edu

Trying... Connected to ARIZONA.EDU.

220 Arizona.EDU -- Server ESMTP (PMDF V4.3-10 #2381)

helo opus1.com

250 Arizona.EDU OK, Tennis.Opus1.COM.

mail from:<trumbo@opus1.com>

250 Address Ok.

rcpt to:<face@arizona.edu>

250 face@arizona.edu OK.

data

354 Enter mail, end with a single ".".

This is where all the rest of the headers go ...

.

250 Ok.

quit

221 Bye received. Goodbye.

$

red sending mailer

blue receiving mailer

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