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I have been running exim4 for years, but I'm in the process of moving to postfix, as postfix is considerably easier to set up all the DKIM, etc., machinery that is now required. Inbound email comes through procmail and is mainly read in emacs (mh-e), which is kind of old fashioned. I have a small script that makes a new email address within my domain for each new use. I sign up for a lot of mailing lists and groups, and my /etc/aliases is more than 5300 lines. I can track if domainA's address starts coming from domainB and disable that address, but that doesn't happen very often, which is a pleasant surprise.

I also have a small script that puts a new sender on my whitelist of sender email addresses. My whitelist is 12000+ lines right now, collected over many years. Procmail sorts to mailing lists and vendor folders, and finally puts things that are not on the whitelist into a "possible spam" folder. From the five or ten items a day, it is easy to spot legitimate emails and I add those to the whitelist. The majority of spam is blocked by the combination of greylisting and DNSBL lists, as the delay of greylisting (ten minutes for me) is enough for them to make the blackhole list, if they happen to ever attempt delivery again.

I was thinking recently that I should be collecting statistics on the use of a lot of those aliases and whitelisted emails, and maybe start garbage collecting my lists.

There are various reputation reports and services that can tell you how your mail is doing in the major ISPs, but a lot of those require higher traffic than a personal or small business generates. There is one service, DMARC[1], that is free and can give you some visibility into how email from your domain is being processed. I put the txt record in my DNS, and Google, Facebook, Comcast, Yahoo, Fastmail, and a few others send me reports about email they have processed from my domain. It's not that interesting at the moment because things are working, but it might help to debug issues if your email was being rejected. At least I see a few spammers are trying to use my domain from their servers.

[1] https://dmarc.org/