Answered by Eliot Davidoff

To find documents associated with a specific email domain, you can run a search using the Organization field. The Organization field stores the domain names parsed out of the People fields of a document. For example, a document with a People - From value of "someone@yahoo.com" will have an Organization - From value of "yahoo.com". 

Another way to see all the People values associated with a domain and search for the related documents is to navigate to the People and Organizations page under Case Setup, and select Organizations in the View by list.