I have self-hosted my own emails many times. Up to having three SMTP servers with failsafe option at DNS.
It’s super nice, but I would never self-host SMTP again. It’s a nightmare. I had to email or open a ticket at most ISPs despite my clean IPs. Most ISPs simply blacklist all IPs unless they are major email providers already.
My advice is go for it but let SMTP be handled by who will deal with these frustrations. MXroute is a great choice and it’s cheap.
In case nginx does not work out for you, you can opt for more generic reverse proxies. frp is my favorite one: https://github.com/fatedier/frp
See https://github.com/anderspitman/awesome-tunneling