Virtual "shared folder"/inbox

Is your feature request related to a problem? Please describe.

Forwarding emails sucks, and shared inboxes are very much a modern standard. Whilst Nextcloud Mail is very forward-thinking in many ways, it feels a little immature in this regard.

Describe the solution you'd like

A shared inbox that allows me to "put" specific emails from my own email accounts into it via drag-and-drop/button, whilst not losing the original email itself from my mailserver account unless I choose to remove it with the action of moving it.

The "shared inbox"/folder would ideally be virtual and exist on Nextcloud, and not on the mailserver itself.

Perhaps it could also "exist", but be use something like Gmail labels.

Describe alternatives you've considered

Alternatives would mean not using Nextcloud Mail, period.

Additional context

I see it as being similar to https://github.com/nextcloud/mail/issues/572, but I don't want to give unfettered access to some email accounts, especially as I receive a lot of email to my personal address that requires sharing with others to figure out a response. Though I do see value in automating it for addresses like news@, sales@ for example, but this task is more about specifying individual emails to go into a "virtual" shared folder that has user input to put emails in there.

Start by reviewing Nextcloud Mail issue #572 and the distinction between copying and moving messages described here. Define the virtual shared-folder or label behavior, including whether originals remain on the mail server and how users explicitly move them. Done means selected messages can be shared without removing originals unless the user chooses to move them.