Configuring an alternative SMTP port
In a lot of cases today your ISP (Internet Service Provider) will block outgoing port 25. Port 25 is used for outgoing SMTP traffic and ISPs block it to avoid SPAM that your account might send. It might seem like a good thing to do but I does cause some confusion and frustration to the end users.
A good hosting provider should run their SMTP services on a few alternative ports. One of the is port 587. Try using it in your SMTP settings and it should work great. Otherwise, you'll have to contact your provider to get that alternative port number.