The External tab is used for external address detection configuration. It will only show if "External Address Detection" is selected in the "General" tab.
External URL - the URL of the external service provider.
External Account - the account needed to access the external URL.
External Password - the password needed to access the external URL. Note that the password will not display in the form, but will be stored in the registry in plain text format. This may be a security problem for some people.
Preceding String - the string immediately preceding the IP address in the file returned from the external service. Note that this string must include any HTML tags that precede the address, not just the displayed text. Regular expressions are supported for this search string.*
Following String - the HTML string immediately following the IP address in the file returned from the external service. This string can be a regular expression.
* - Acknowledgement for regular expression support is given to Andrey V. Sorokin. He has some documentation for his regular expression evaluator at his site.