I am looking for a function "mark message unread when dragging on tab" nice
would be if this could be set in the tab specific settings.

We have a company wide e-mail adress and from some employees I have a tab of
their inbox, when I drag the read message, I would to be sure that the message
is unread when they open their inbox.

Sounds very specific, but I can see the benefit in your specific case. Note
that the folder specific properties will be applied to the _folder_ [not just
the QF tab, which is just a useful UI for such folder specific extensions] (so
setting an email to unread would likely also happen if you dragged the email to
the folder using the folder tree and maybe even when moved by a filter action)
- I assume that it would still be useful for you in this case.

Created an attachment (id=8693) [details]
4.17 prerelease 31

Here is a prototype with the new checkbox (still hardcoded in English, to be
submitted to translators) 

I only tested what happens when I drag the email into a folder via a tab; I
think all manual moves of Email should be supported. but I wouldn't be
surprised if it would work for filtered emails as well (to test).

Implemented in Version 4.17 - released on 05/11/2019