See this howto: https://poolp.org/posts/2019-09-14/setting-up-a-mail-server-with-opensmtpd-dovecot-and-rspamd/

I have delivery to the inbox of all major providers using this. Email is not that hard…

Been hosting my own email for over 20yrs. Get a vps at some reputable hoster, and make this a dedicated mailserver. Be sure to setup all dns records that are required, and rollout antispam measures.

Thing is, you grew up in the pioneering age of computing, and in that time you needed to do everything yourself. This gave you a bunch of skills for free, that are hard to do today, because most of the hard stuff is automated away and snuck behind a gui and/or containers.

Alma, Talos, OpenBSD

OpenLDAP multi-master with a bunch of custom schemas.

Can you explain what you mean with lightweight?

You expressed yourself just fine and my question is still valid. Do you have the capacity to handle multi Tbit traffic on the edge ips that you use to hide the backend ips? Because if all of those are flooded, not only will the backend app be unreachable, but all your customers will be unreachable as well.

Even if you can get the appZTNA stuff to work (which I doubt), how is your infra going to absorb multi Tbit traffic without customer impact?

You will be in for a surprise once you learn about tcpdump ;-) Welcome to internet hosting!

http://www.catb.org/~esr/faqs/smart-questions.html

Read the changelogs from 1.5.3 to 1.5.5 and see if you need to take additional steps

ngircd has the concept of a global password. Distribute this password and you’ve got a simple psk based acl mechanism

what error message are you getting?

It all depends on what you do with the box, how the applications you run utilize the cpu (single vs multithreaded/multiprocess but also stuff like cpu cache utilization. if you profile the workload that you want to run (see if its cpu, memory or io bound for instance) will help you in figuring out what works best for you.

Have a look at mailcow if you’re new to MTA’s. Use that and a (sub)domain to figure out how to set things up. Once youre satisfied with the setup, reconfigure your domain on the new MTA. Use a mailclient with $yourformat and imap support to import your old email.

And above all, dont be discouraged by the naysayers that think its an impossible task; Its not, but it is complicated to get right bc all the parts involved ;-)