Indeed it's not a great idea to rely on 3rd party services for allow/block-listing. You're giving power to those 3rd parties, and it centralizes email. Ironical

Indeed it's not a great idea to rely on 3rd party services for allow/block-listing. You're giving power to those 3rd parties, and it centralizes email. Ironically, quite some people running their own mail servers use blocklists, pushing deliverability problems due to being blocklisted onto fellow self-hosters. Another reason why it's not great to use allow/block-lists: You're passing the IP's of everyone you're communicating with to those 3rd parties. In mox (a mail server, I'm the author), junk filtering is first done based on known good/bad reputation of the (verified) domain of the address of the sender, based on classifications made by the user (and mox helps with those classifications). That means everyone you've seen good/bad mail from before, can quickly be classified without the need to contact any allow/blocklist. For first-time senders, a bayesian content-based classification is used. That is almost always is good enough. But you can also configure blocklists. They will only be consulted as long as there isn't enough reputation for the sender. Once you've corresponded with someone a few times, the blocklist isn't used for their messages anymore.