The first thing to check on your server, is that the IP/network
you are connecting from is not blocked by any firewall configurations
you may have. If you have verified this, then the next step would be
try and connect manually to your SMTP server. This can be by bringing
up a command prompt and typing the following (assuming that your
servers IP is 1.2.3.4):



telnet 1.2.3.4 25 <enter>



A banner should come up pretty quickly after you hit enter. If all you
see is a black screen, and the connection eventually times out, you
will need to contact your ISP. Many ISP’s today block outgoing
connections to port 25 to servers that they do not control. Verify with
them if they are doing this or not. If so, many ISP’s will allow you to
opt out of this measures.