I’m not familiar with the ellipse doing what you’re referring to so. I think maybe this is if it’s hiding content from a long message that has previous content. But it’s not technically the other email. It’s an extension of the current reply thread. If that makes sense
If I’m wrong, here’s some other ideas (not fully knowing what you’re wanting)
Check and see if “conversation view” is turned on. View / Messages / Conversations / Group into conversations.
Thats how you get the related messages to group together and use the expansion carrot to expand and contract the group of messages.
If you want messages to stack, then you’ll go to View / View Settings / Message organization and select either Newest on top or Newest on bottom. If you have Show each message separately, that will cause the messages to not be stacked.
