Detail
You must specify the WebMail login address in your remote web browser as follows
http://Internet_IP_Address/webmail
If you have a domain name registered against that IP address then you should be able to specify
http://YourDomainName.com/webmail
If these methods do not work then check to make sure that your web site is configured in IIS to be available on the internet interface. In IIS look at the properties for the Default web site and on the Web site tab, the IP address field defines the interface that the web is available on. You need to make sure that this includes your internet IP address.
If you still cannot access your website remotely, ensure that you do not have a firewall that is blocking port 80.