Some ISP's have a policy of blocking port 25 which is used for SMTP.  The following can be done to test this:

 

1. In Windows go to the Start Menu then select 'Run...'. 

2. Type: telnet domain.com 25 (where domain.com is replaced with your domain name)

 

You should see an ms-dos window popup with an Exim welcome message (the software we use for email on servers).  If there is no message it is possible that your ISP blocks port 25.

 

If your ISP does block port 25 we can bypass this by allowing the use of another port for SMTP (usually port 26).  To see if your server is already setup for this follow the same steps again and enter 'telnet domain.com 26' (without quotes).  If still no welcome message please open a support ticket and we will open port 26 on your server or look into the cause of the problem.

 

Following this you will be required to change the port for SMTP in your email software.  Please consult the documentation that came with the software to do this.