I don't have the grouped boxes but I use a sieve filter on my ISPs mailserver to automatically create folders based on prefix@mydomain.example
Here is my script:
require ["fileinto","imap4flags","variables","regex","mailbox"];
## A catch all filter designed to automatically organise emails sent to a catch-all address into a folder based on the receiving address e.g amazon@example.com --> INBOX.Amazon ## If the folder doesn't exist it is automatically created
if exists "X-Delivered-To" { if header :regex "X-Delivered-To" "([^@]+)" { set :upperfirst "prefix" "${1}"; fileinto :create "INBOX.${prefix}"; stop; } }