Whenever new emails come in on an existing thread, I like to be able to review the previous emails - including ones that I sent. In gmail, this can be done w/ their threaded conversation view… basically anytime an email comes in, it is automatically grouped and viewed with all the related emails. In outlook, they support this by having a ‘find all related messages’ button on emails. When clicked, it does a search and pops up a list of all emails (inbox, outbox, sent, etc) in the thread. You can then open the emails separately to view.
Would love to see all related messages together somehow. Whether it’s in a threaded/tree conversation view, find-related-messages functionality, or something new!