Solved! Go to Solution.
Rajesh, you could use a new beta feature called "Munchtions" that allows you do add functions to Change Data Values. One function is "regex replace", which allows you to extract the domain from the email address (and many other things). This would be the syntax:
You will have to ask Support to enable this feature.
Once you have the domain in a separate field, it should be much easier to count the number of unique domains, for example a Lead Performance report grouped by "email domain" (time period: all time).
MODERATOR EDIT: This feature is only available for internal use. Support is not able to enable this for customer use at this time.