I am an EarthLink/MindSpring customer and can't send email 

When you attempt to send email through mail.yourdomainname, your email program is using what's called "port 25". EarthLink and MindSpring have blocked this "port 25", making it impossible to connect to mail.yourdomainname and send email.

The solution in this case, would be to send email through mail.earthlink.net or vipmail.earthlink.net. Should you have any questions about EarthLink and MindSpring policies, please don't hesitate to get in touch with their technical support department.