We need a way to keep labels when we archive a mail.
Actualy, if we navigaite under a label, and open a mail that has only this label (not even in Inbox any more), and we click the "archive" button, it will simply remove the label. It should not be so ! We do need to be able to still find the archived mail by label.
There are multiple ways to achieve it. For example by moveing archived email to an "Archive" folder and keeping labels in that folder. Or you can also add an "archived" flag, with posibility to filter by this flag. And for sure there are many other ways to achieve it.
In fact, we don't realy care about the way to do it, but we do need a way to do it.