$> telnet localhost smtp

Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 mailtest ESMTP Postfix (Debian/GNU)

$> ehlo example.com

250-my-new-mailserver
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN

$> mail from:<nico@example.com>

250 2.1.0 Ok

$> rcpt to:<admin@example.com>

250 2.1.5 Ok

$> data

354 End data with <CR><LF>.<CR><LF>

$> Hi Admin,
$> 
$> What's up ?
$> .

250 2.0.0 Ok: queued as A9D64379C4

$> quit