Re: "Apple Mail: Often, when I open an email
there is an older, archived email piggy-backed above the new, incoming email."
We can customize many features in MacOS Mail app., or just use the default settings.
Apple Support's online article for MacOS 15: View email conversations in Mail on Mac - Apple Support
Eg: says:
"By default, Mail groups together email messages that are part of the same “conversation” (or thread), instead of listing each reply individually. Conversations make it easier to follow a thread and help streamline your Inbox.
Tip: It’s easy to turn conversations on or off. In Mail,
choose View > Organise by Conversation (a tick shows it’s on)."
Change Viewing settings in Mail on Mac - Apple Support
Eg: says:
"When viewing a conversation, show related messages (those located in other mailboxes).
"choose Mail > Settings, then click Viewing. > include related messages
Useful Resource: Mail User Guide for Mac - Apple Support