I've been hosting and operating my own MTA MX with Postfix since 2005. I have Postfix set to use "MailDir" format storage (one file per email) and then use Procmail filters to direct emails into per-sender or per-topic specific folders when they arrive on the server - nothing needed to be done in the email client. Dovecot provides the IMAP4 client interface. Thunderbird connects via IMAP4.
Each domain has its own user home directory so for each there is a /home/${domain_name}/Maildir/ directory as the base for storing emails, and each IMAP4 folder has an associated directory. Snippet:
Each domain has its own user home directory so for each there is a /home/${domain_name}/Maildir/ directory as the base for storing emails, and each IMAP4 folder has an associated directory. Snippet:
Here's an extended snippet example from $HOME/.procmailrc that directs deliveries into the correct directory (IMAP4 folder):