Do any of the following in a conversation in the preview area:
Step through messages in a conversation: Press Option-Up Arrow or Option-Down Arrow.
Show more of a message: If a reply contains the original message but doesn’t show all of it, click the See More link at the bottom of the reply.
Change the order of messages in the preview area: Choose Mail > Settings, click Viewing, then select or deselect “Show most recent message at the top.”
Exclude emails from a conversation
By default, a conversation includes related messages that are in other Mute email conversations in Mail on Mac