Buy your own domain and run mox (https://github.com/mjl-/mox) on it. In the setup it provides details on the DKIM info you need to put into your DNS records. Get a PTR record from your ISP (if hosting at home); periodically check your blocking from spamhaus etc.

I run mine on a Pi4 no problem whatsoever, but I guess a VPS could also be used, although the scamalytics analysis will show it's a server or an IP shared with an anonymising VPN etc. if it's a shared IP on the host.