Go to Subscribers and click on Manage Subscribers. Type in the email address and click Search for Email Address. You can also click on the letter in the list above the search fields to display subscribers with email addresses beginning with the letter or number you select.
You can also enter a portion of an email address and do a search. For example, you can type “info” and click Search for Email Address and all email addresses that have “info” in them will be displayed below the search fields. This can be useful for finding email addresses that are invalid so you can clean your list. You can also search for email addresses under a particular domain this way: type hotmail and all addresses at that domain will display.