#install mail tools
$apt-get install mailutils
#install telnet client
$apt-get install telnet#telnet some_ip port
$telnet x.x.x.x 25If you get an output, it's means the smtp respond !
$mail -s "Test Subject" address@domain.com < /dev/null$cat /var/log/mail.log#telnet x.x.x.x 587 or 25
HELO < you start conversation
250 OK < server lets you proceed
MAIL FROM: <someuser@somedomain.com>
250 OK < server is fine with this sender
RCPT TO: <someuser@targetdomain.com>
250 OK < server is fine with recipient
DATA < you are going to send email body
250 OK < server is fine with that - proceed
Here you send your message
. < need to close the DATA by the dot !
250 OK < server accepted message
QUIT