Email messages are neatly grouped into conversations. If there were back and forth replies to an email, tapping that email expands and shows its series of messages.
To check your email from all your accounts just in one place without having to switch to different accounts, you can link your inboxes as one.
The default name for your unified inbox is
Next time you want to check your email, tap
Linked inbox on the Start screen or in the apps list.