Change account based on who you are sending to (email address history).
There are some existing ideas that come close to this idea, but not exactly. I would like the account I am sending from to automatically switch based on who I am sending my email to. For example, if I am sending an email to my friend Dan (email@example.com), I want it to be sent from my personal Gmail account. If I am sending an email to a partner or employee, I want the email to be sent from my business account.
The way this would work is look back (or record) the mapping of from which account to which email address. If I change my from account for a certain email address, use that account going forward when sending to that email address. Otherwise, just use the default address.