The new Send experience is being improved to support predictive email addresses based on the agreements that load into the Manage page when you log in. Every email address that is associated with every agreement in your Manage tab, be it a sender, recipient or CC’d party, is indexed.
When you start to type an email, all of the potential matches dynamically list alphabetically, allowing you to enter only the first portion of the email, and then use either keyboard arrow keys or your mouse to select the address from the list.
Using the mouse populates the Recipient with the selected email address, where using the arrow keys lets you move the focus through the list, and then either Tab or Enter selects it.
The index is built when you first log in. If you send an agreement to a new email address, it will not be added to the index until the next time you log in.