While sending an email from an account in Lightning using the standard Activities email component, the address lookup appears to first pull matching users ("Bob" in my example) from account contacts, then pull other contacts from other sources, including other accounts. If we don't have any account contacts, it will just pull from other sources:
It's easy to see how this could be a problem if you accidentally select a "Bob" from the wrong account and send him sensitive information about your intended "Bob".
Is there a way to limit this component to just show contacts related to the account you are sending from?