This field contains the contact's e-mail address.
If you have specified an interaction template for e-mails in the Relationship Management Setup window, when you send an e-mail you can log the interaction in the Interaction Log Entry table.
To the right of the E-Mail field, there is a button with an envelope. When you click that button, the Create Mail wizard appears where you can write the e-mail and create an interaction to record the e-mail in the Interaction Log Entry table.