Improve deleting a domain by clarifying the specific email addresses used on the domain

[d19dotca]

I am trying to delete a domain from my Cloudron instance. It tells me this when I use the API (and similar when using Cloudron GUI):

{
  "status": "Conflict",
  "message": "Domain is in use by one or more mailboxes. Delete them first in the Email view."
}

It took me a while to remember that I had used the domain as an alias on my own domain mailbox for the postmaster and such emails. It'd be very helpful if the error reported here was much more useful because it could theoretically be used anywhere and when managing 20+ domains, it's not immediately obvious where that may have been used if not on the actual mail domain itself. Would love to see this improved to be more specific on what mail domain(s) contains references to the domain I wish to delete.