below is the testing I did on my linux box
$ telnet localhost 25220 redhat.localdomain ESMTP Postfix
mail from: email@example.com
250 2.1.0 OK
rcpt to: nonexsit
550 5.1.1 <nonexist>: Recipient address rejected: User unknown in local recipient table
250 2.1.5 OK
354 End data with <CR><LF>.<CR><LF>
Subject: hi this is subject
this is email body
250 2.0.0 OK: queued as 25AE12AD1
221 2.0.0 Bye
in /var/spool/mail/tom will see the email we just sent
please note the lines starting with numbers are the output returned by SMTP server, the numbers are the status code, search "smtp status code" for more details.
"ehlo", "mail from:", "rcpt to:", "data", "quit" are the commands sent to SMTP server.