In InStream you can add several email addresses to one contact. Add all email addresses, to monitor all communication with this contact.
Step 1: Open the “People” tab
Open the “People” tab, and select the contact to which you want to add next email address.
Step 2: Open selected contact
Open selected contact and click on the “Add” button in the “contact details” section. Next, type in the new email address and click save.
Read more about contact detailed view.