clear distinction between new and old parts of threads

[lseeman]

To requirement 16 C

The grouped threads often repeat the original message which is hard for slow readers. It can be very hard to tell what I have read already. This is often why I lose threads or emails, and the grouping often repeats the original message so I can not tell what I have read already.

Suggestion: Make a clear distinction between new and old parts of threads, without repeating them, so the user can track what they have already read. Use headings where possible.
The subject / label/ header needs to change when issues start to get discussed so that the user can find the new topic and track what they have read.