Its amazing that we have labels. I think I have waited for this for a few years now (since 2015).
Some suggestions on the same though:
I extensively use Outlook mail client and it is not built for labels.
Just to test, I added a few labels to a message
So message had two labels A,B
In Outlook, deleted the message in "B" folder
In FM, message existed in "A" label and had a label of "B" when opened. However, when I click on "B" in the label pane, the message had disappeared. Something was broken when a copy was deleted in Outlook.
I think we should have some sort of separator between system labels (Spam,Deleted, Sent, etc) and user labels.Trash folder or a label is gone. I guess we need that restored as a system label.
I have just used this for maybe 30 mins and these are initial thoughts.
Post title reminds me of "Thanos is coming!"