From the main dashboard, click on "Sender Signatures" in the top left.
To add a new sender email, click "Add Signature" in the bottom left, this will bring up a form that allows you to set your "From" email, "From" name, and "Reply to" email. Please note: "From" email must be unique:
Once a sender signature has been created, you can edit to the "From" name and the "Reply To" email at any time by clicking the box on the main "Sender Signature" screen. The main "From" email cannot be changed.