Simple and clean backup mail server

This is backup incoming spooler mail server. Made to work somewhere in the wild buffering incoming email while the primary server is not accessible.

Installation

Build from source

git clone https://github.com/kandev/mx2
cd mx2
docker-compose build
docker-compose up -d

Get the latest image from Docker Hub

docker create -h mx2 --name mx2 -v /etc/localtime:/etc/localtime:ro kandev/mx2:latest
docker start mx2

Configuration

Host server

Usualy I disable all the fancy things which Docker does with iptables by adding this to /etc/docker/daemon.json:

{
  "userland-proxy": false,
  "iptables": false
}

I prefer to do all the firewalling manually.

Obtain SSL Certificate

It's not compulsory, but it's good practice to have trusted certificate. Initial creation of the certificate is manual.

certbot certonly --agree-tos -n --standalone -d mail.domain.tld

Daily cron job is running to automatically renew any expiring certificates.

Postfix main.cf

Update myhostname, proxy_interfaces and relay_domains in /etc/postfix/main.cf.

Final notes

I have included SPF filter, some of the most reliable black lists and basic sender filter which should be enough to keep the major part of the spam away. You should add mx2's IP to mynetworks or SPF whitelist on your primary mail server.