My personal domain has hundreds of aliases - one for each site I deal with. This is great for identifying the source of spam, and I retire any aliases that get spam.
haveibeenpwned.com lets me add a domain, but wants 3912 USD a year to actually tell me which addresses leaked. This is obviously an insane price for a nice-to-have.
Is there an alternative for free or very cheap? A self-hosted tool that would pull down lists would be great, but I suppose those lists aren’t public.
Maybe not an exact fit for your situation and would take work but I use addy.io. solid and have had no issues with it for 4+ years.
If it takes me on average 5 minutes to login and change an email address, it would take me about 1 days, 18 hours to change them all! It definitely looks worth it for others who want to start using aliases.