mail. Since I don't trust Google or pretty much any "free" provider at this point, that means doing it myself. Some steps (registering a domain, ordering business-class service or a static IP, etc) are self-evident. But after that, there's a lot I really need to learn
Running your own inbound and outbound SMTP service on the public network is not as easy today as it was 10+ years ago. You need to play with SPF, eventually DKIM and DMARC (and the many false-positives you get bounced back caused by mailing-lists subject and signatures), leverage DNSRBL (real time blacklists), ideally enforce STARTTLS and accept the fact that nobody cares about certificate validation on that front. Not mentioning having to deal with Gmail and Microsoft's very agressive blacklists (up to the point where it seems to be whitelists or at least reputation-based). Same goes for DNS. If you want to host your own, it's a whole new game now with DNSSEC.