Nextcloud in the club / Share e-mail account for specific user group

Hello all,

We are currently digitizing our club and are using Nextcloud/Storage-Share from Hetzner.
So far, everything is working really great.
We now have Collectives, Deck, Photos and Office running.

Now my wish would be that every board member (user group board) automatically has access to the mailbox
I can’t get this to work with Nextcloud’s normal mail app.
Is there a way to share mailboxes with other users?

Or do the users really all have to include the mailbox themselves?