Avoid remove of messages but able to move them (same for concepts)

Hi guys.

I'm trying to avoid people removing messages but allow moving them.

The issue here is that moving disallows removal at the moment (same
for concepts) and I get duplicates on moves in the old folder it stays
and in the new folder it's copied.

This is done by ACL and people cannot remove messages.

Any idea how to accomplish this or at least be able so people cannot
remove them from trash ?

Thanks!

Matt