SMTP is port 25. Might want to try changing the port number.
Also their mail server may be configured to only allow smtp connections from certain nets. If your webserver is on the same machine you are running outlook on that shouldn't be a problem, but if it is hosted else where that could be your problem. It could also be blocked by a firewall on your end or their end.
You might want to try telnet to the mailserver and see if you can hit it.
note: I can hit mail.roomsquare.com on port 25, and I receive the following:
220 mail15.mijndomein.nl ESMTP Exim 4.69 Tue, 10 Apr 2012 20 +0200
So chances are its just the port that you are using.