External Host Path
This optional setting is available in Options Tab.
It allows replacing the host portion of the {sitelink}, {itemlink} and {itemurl} tokens that are inserted in e-mail alert messages. It is usually used to provide SharePoint users logged in from external local domain with a public host path to the SharePoint web server.
For example, if you enter http://wssportal.yourcompany.com/, outside users will receive alerts with links on item but site links in their e-mail alerts will be changed from http://YourInternalServerName/ to http://wssportal.yourcompany.com/... and will be available for those outside of the network.
