I’m looking at the latest update, but I’m still unclear on the “Introduce filtermail-transport for delivering messages via HTTPS (SMTP stays as fallback)” scheme. So, does this mean we’re using Nginx on port 443? I’m also curious if this will replace port 25 (federation) in the future?
Yes, nginx acts as a reverse proxy to deliver messages to the filtermail-incoming process.
No, it will not replace port 25 and SMTP. If you are setting up a chatmail relay, it’s still best to make sure that the server can accept connections on port 25 and make outgoing connections on port 25.
You can setup a relay on a server that has port 25 filtered out, but it will only be able to speak to servers supporting HTTPS delivery. There are madmail servers that are set up like this and supporting HTTPS is essentially a compatibility mode for talking to them.
Some hosters however throttle port 25, so delivering most messages over HTTPS avoids this, this is probably the best use for HTTPS delivery.