Sometimes when you’re looking at a recent email it can be handy to be able to quickly refer back to earlier messages in the same conversation. While the “Organize by Thread” option (found in Settings under Mail, Contacts, Calendars) can be helpful if all of your messages are in the same folder, this is often not the case, particularly when it also involves messages you’ve sent, since these usually remain in the “Sent” folder for most users.
Fortunately, iOS 8 has a handy little feature that can be used to search out your Sent Messages and include them in the conversation thread. If you swipe right-to-left on an email message you’ve replied to (or an email that’s a reply to one of yours) and tap the “More” button, you’ll see a “Show Related Messages” button that appears with the rest of the additional options. Tap on this, and Mail will provide you with a conversation view of your correspondence with that person and anybody else in the thread. As an added bonus, it even notes which messages were replies or forwards, and who they were forwarded to.
Keep in mind that unlike the OS X Mail app, this doesn’t seem to work across your entire mailbox — it mostly seems designed to ferret out messages from your Sent folder.