How can I efficiently manage invoices from multiple email accounts?

I'm currently managing invoices and documents coming from several email accounts and need a reliable way to organize everything without losing important files. My current setup involves forwarding all emails to a single mailbox and using a Python script that connects via IMAP to extract attachments and route them into a structured folder tree in Nextcloud. However, I'm facing challenges with avoiding duplicate processing, ensuring the setup remains stateless from the mail server side, and dealing with inconsistent file naming from different senders. At the moment, I use YAML rules for routing, SQLite for local state, and checksum-based deduplication. I'm looking for ways to improve classification and routing. What strategies do others use? Do you prefer strict rules, metadata extraction, or perhaps leveraging machine learning?