Update: Maybe I'll Dump Spamhaus Too 2020-07-13
Well, I am happy to announce that I am pleased with the performance of junkemailfilter.com and am using it as my primary DNSBL. I have justspam.org setup as my secondary DNSBL but frankly only a handfull of connections are dumped per day by that one. That doesn't mean it isn't effective, it just means that junkemailfilter.com catches a lot of crap first. They also have some other features like backup MX and hosted email. I have not tried them, but they might be worth a shot. If anyone has any feedback on those other features I would love to hear about it. So... if you use Spamhaus maybe you should consider switching too. Just sayin'.
Maybe I'll Dump Spamhaus Too 2020-06-27
A DNS Blacklist is a way for people who run email servers to reject mail quickly based on the IP address that is trying to send a message. Basically the receiving mail server will use a DNS lookup to ask a remote DNSBL if the sending mail system is a spammer. If the DNSBL says "I never heard of them" then the receiving mail server proceeds with the mail transfer, but if the DNSBL says "I know that machine" then the receiving mail system just rejects the message and disconnects. The thing is, those DNS Blacklists are run by various individuals and organizations, with varying degrees of trustworthiness and enthusiasm for correctness. Many of them whitelist the "big mail providers" in order to minimize the risk of incorrectly flagging an IP as bad, but what about the little guy?
I run my own mail server. I spend countless hours jumping through hoops in hopes that wankers like Microsoft will stop flagging me as spam. I have setup SPF, DMARC, Domainkeys, rDNS, and some other acronyms that don't mean anything to most people. Blacklist operators don't much care though... I guess it isn't worth their time. So I have to monitor blacklists and hope my ass doesn't get flagged. The bad news is that Microsoft's spam evaluation is so garbage that I will get flagged anyways.
So, having said all that... my mail server got flagged as a spam source by Spamhaus. Well actually Abuseat, which is a division of Spamhaus. Clearly the goal of every tech company is to be bought by a bigger tech company. Anyways, Abuseat figures I was sending spam at Tue Jun 23 22:05:00 2020 UTC +/- 5 minutes and went on to say that after 72 hours my listing would expire on its own. Bad news, there was no mail sent out at that time, and the blacklisting didn't expire after 72 hours. Fail.
So today I spent a little time doing removal requests, and a lot of time filling out captcha puzzles because DNSBL operators obviously have a rampant problem of people trying to get themselves delisted. Really? That's a thing? Anyways, I have been getting a fair bit of mileage out of junkemailfilter.com and justspam.org lately, and have dropped spamhaus from my mail server. I'm going to let it run like that for a week or so and see if it affects my inbound mail at all. I don't think it will. If you run a mail server, maybe you should consider dumping Spamhaus too... just sayin'. :-)