When clicking on a link in an email, the Active Directory automatic passthrough authentication (enabling the user to log in without having to type their credentials) fails to work. Manual authentication works, however.
This is a known limitation of ServiceDesk 7.0 and does not work. The only method of Active Directory automatic passthrough authentication that is currently supported is by going directly to Process Manager (http://server_name/ProcessManager).
Note that in ServiceDesk 7.1 'if passthough authentication is setup correctly' the email link does work.