Generally, when you do a search in Mail you don’t need to know
where the files reside. When you remove an email using the Email
mail messages
search options, Tidy Up will tell Mail to delete the
email record of the removed email file. So, in this case, if you are
sure that the result list contains true duplicates and you do not need
to know where the files reside, you can remove the content of the
default box All but one item of each duplicate group
.
This is also applicable using the An item of each duplicate
group
smart box.