Email -Test smtp via telnet

Open a CMD prompt
type  TELNET MAIL.THEIRDOMAIN.COM 25 

You should see something like this as a response:
220 mx.google.com ESMTP 6si6253627yxg.6

test sending mail:

ehlo mydomain.com
mail from:<fedrik@mydomain.com>
rcpt to:<recipient@theirdomain.com>
data 

"This is a test, please do not respond "
.
quit