What feels the most like classic email clients is the way they abstract recipients by placing the contact's name into a box and no longer display the email address next to it. The pretty box is fine, but I hated seeing contacts on an email in something like Outlook and not being able to quickly confirm which address was used for that contact, so perhaps it'd be better if they had these recipients in a scrollable list.
I often need to write emails with specific details from other threads. this is way way faster than save draft, search, copy, go back to draft, and paste.
Maybe there's a better workflow for this problem - but the draft saving way sucks.