Have you ever had a tough time finding where an email address exists in your Exchange Org. Often times this comes from have a forward on a mailbox or a contact set to an external address. If you run the following in your Exchange Management Shell, you should be able to find almost any address or portion of address in your org. I like to format the output too, so you can change the | format-table part to however you would like the output to read.
get-recipient -filter {emailaddresses -like "Pattern goes here"}|format-table name,recipienttype,emailaddresses
