Spamgourmet is amazing and has been really responsive when it comes to fixing the sorts of issues that come up when running an email service (e.g. blacklisted IPs, messages getting shunted to spam, etc). I've been using it since 2007 and it's kept more than 10,000 junk emails out of my inbox. I think it actually started almost 20 years ago.

Unfortunately the operator of the site is really sick and has talked about shutting the site down. Last I heard he'd found someone who seemed trustworthy to run the site when he isn't able to, so we'll see.