Some email providers and postfix also allow the creation of dynamic aliases of the form user+alias@example.com.
One thing I noticed is that most mailing lists now have a header that identifies them with a specific ID. When I click "Make rule from this email" in Fastmail the primary option is to sort it by that header, not by the sender or receiver. That way only the marketing emails get redirected and not transactional ones from the same sender.
List-Id: A Structured Field and Namespace for the Identification of Mailing Lists
Do they? I think the local part can be anything that the MDA chooses to accept and that different local parts of an address result in the email message being placed into the same mailbox, is nothing an RFC would forbid.