In Windows, if you go to Start -> Run -> CMD then at the prompt type:
Make sure to replace yourdomain.com with your actual domain name. If you see something like this after you run the command, then you're OK.
telnet smtp.YOURDOMAIN.COM 25
Then you can type
220 xmailXX.myhosting.com ESMTP 648143d3667b3045487bb901cdbbf649
And close the window. If you don't see the response from myhosting.com, then your provider is probably blocking port 25. In some cases when your ISP blocks port 25, you can use our Alternate Port SMTP instead.