Email servers are notoriously difficult to configure, hence all these solutions ranging from tutorials to "everything included" systems. Recent activity on HN about mail servers: Mox, Poste.io from yesterday [1], Mailinabox, mailcow, ispmail, maddy, stalwart jmap, etc.
Many of these systems keep redoing the same work over and over which seems wasteful.
What I'd like is a "mail reverse proxy" that does all the work to manage DNS, SPF, DKIM, DMARC, etc and handles sending and receiving emails, but doesn't do any storage or user management. Instead it forwards mail from/to the "real" mailserver sitting somewhere in a private network. (Maybe using LMTP [2]?)
This way you could roll the dice until you get a $5 VPS with a clean static IP and just park it there permanently, where it does nothing but sends and receives emails from your real mail server wherever you want to host it. Kinda like a PO box. You never have to worry about upgrading it to get more storage, or switching providers and losing your IP, if it gets hacked the worst it can do is spy on live email traffic and send spam until its patched.
Why doesn't this exist already?
> Many of these systems keep redoing the same work over and over which seems wasteful.
There certainly is duplication of effort, but all these systems try to bring something new to the table.
> Why doesn't this exist already?
Because you haven't written it yet? (;
But seriously, I've had a somewhat similar thought. But instead of running a "reverse mail proxy" on a VPS, I was hoping to take a VPS, set up some tunnel magic (with wireguard probably) that forwards all traffic coming in from the internet, intact with original IPs, to my local side of the tunnel, and vice versa. So my local machine just has the same public internet IPs configured as the VPS and all internet traffic is going through the tunnel. So just use a VPS for its IPs. That way my data is not stored at my hosting party. If anyone has set this up already, or thinks this is a bad/good idea, I'd like to hear.
- https://bore.pub && https://sslip.io - https://github.com/juanfont/headscale
I don't think there's anyone using this kind of tools for emails, the technical limitations elude my understanding TBH. This comment might be border to off-topic, but I think the tools fill in the niche use-case you just mentioned. Have fun!
edit: might be of your interest to check this list! https://github.com/anderspitman/awesome-tunneling#recommenda...