Yeah, you’d need to use some other address that you forwarded through a filter and then to your Discourse mailbox. I’m pretty sure that you can use something other than their mailbox if you wanted to, but forwarding to the existing mailbox is probably easier.
The fact that the premier tool to solve your problem hasn’t been updated in 20 years says a lot, I’m afraid. If you ran it through a gmail account you could use its filters and then forward to your existing mailbox. I’d think that you already have some such forwarding in place if you’re getting mail delivered to a category.
I used to make decent money managing mailing lists. I think they’re pretty much a bad idea held on to only by old people not unlike me.