I’m a younger person (32) and didn’t know about this norm until I saw an older person doing it. Now I do it as well but make it obvious what the intent is.

For example:

Hello (person),

See responses below in red

Blah blah blah original email text

Red text

Blah blah blah

Red text

Etc.

It works really well. Said person will even respond in green to my red. We do all this in new outlook, which to be fair, is still a mess for other reasons. Don’t even get me started on the search lol