One fundamental paradigm difference between texting and email is that every email client I know of groups messages by account, then folder/tag, then (sometimes) thread, while every messaging app I've ever used groups by contact/sender.

I can send and read emails from my phone just as easily as texts.. but why don't I? At least in part because conversation by contact is a much nicer way to do initial filtering than dumping everything in an inbox.

I don't suggest that we try to turn Geary into a messaging application -- an email is still an atomic unit and we shouldn't try to split the title and the body, or show the entire contents of multiple emails in in a conversation view. But sorting by contact would be very useful.

I suggest adding a way to view a list of email addresses that have sent you mail **that is in your inbox** (of any account). It would go in the left pane, where the "Inboxes" menu is. One option is to add this list as "Inbox - Sender" and change "Inbox" to "Inbox - account" (or something like that); the other is to add a setting that toggles between inbox by account and inbox by sender. Either way, when you click on an name/address in that list, the second pane fills with messages in your inbox from that contact, replacing the sender name/address with the account through which you received the email.

When composing in this view, follow the following rules for pre-filling fields:

Send TO the sender's address (duh).

If the sender is only known to one of your accounts, send FROM that account.
Otherwise, if a conversation with that sender is highlight, send FROM that account.
Otherwise, send FROM the account from which you most recently corresponded with the sender.
  - There will always be a known most recent correspondence because the sender will only appear in this list if you have an email from them in one of your inboxes.