Adding the docker network's gateway to the list of trusted hosts, e.g. using the `network` or `connected-networks` option, can create an [**open relay**](https://en.wikipedia.org/wiki/Open_mail_relay), for instance [if IPv6 is enabled on the host machine but not in Docker][github-issue-1405-comment].
For more details about the environment variables that can be used, and their meaning and possible values, check also these:
- [Environtment Variables][github-file-env]
- [`mailserver.env` file][github-file-dotenv]
Make sure to set the proper `domainname` that you will use for the emails. We forward only SMTP ports (not POP3 and IMAP) because we are not interested in accessing the mailserver directly (from a client). We also use these settings:
-`PERMIT_DOCKER=network` because we want to send emails from other docker containers.
-`SSL_TYPE=letsencrypt` because we will manage SSL certificates with letsencrypt.
- We need to open ports `25`, `587` and `465` on the firewall:
```sh
ufw allow 25
ufw allow 587
ufw allow 465
```
On your server you may have to do it differently.
- Pull the docker image: `docker pull tvial/docker-mailserver:latest`
- Now generate the DKIM keys with `./setup.sh config dkim` and copy the content of the file `config/opendkim/keys/domain.tld/mail.txt` on the domain zone configuration at the DNS server. I use [bind9](https://github.com/docker-scripts/bind9) for managing my domains, so I just paste it on `example.org.db`:
```txt
mail._domainkey IN TXT ( "v=DKIM1; h=sha256; k=rsa; "
"iqq3bD/BVlwKRp5gH6TEYEmx8EBJUuDxrJhkWRUk2VDl1fqhVBy8A9O7Ah+85nMrlOHIFsTaYo9o6+cDJ6t1i6G1gu+bZD0d3/3bqGLPBQV9LyEL1Rona5V7TJBGg099NQkTz1IwIDAQAB" ) ; ----- DKIM key mail for example.org
Then don't forget to change the serial number and to restart the service.
- Get an SSL certificate from letsencrypt. I use [wsproxy](https://github.com/docker-scripts/wsproxy) for managing SSL letsencrypt certificates of my domains:
./setup.sh alias add admin@example.org myemail@gmail.com
./setup.sh alias add info@example.org myemail@gmail.com
./setup.sh email list
./setup.sh alias list
```
Aliases make sure that any email that comes to these accounts is forwarded to my real email address, so that I don't need to use POP3/IMAP in order to get these messages. Also no anti-spam and anti-virus software is needed, making the mailserver lighter.
./setup.sh alias add admin@example.org admin.gmail@example.org
./setup.sh alias add info@example.org info.gmail@example.org
./setup.sh alias add admin.gmail@example.org myemail@gmail.com
./setup.sh alias add info.gmail@example.org myemail@gmail.com
./setup.sh email list
./setup.sh alias list
```
This extra step is required to avoid the `553 5.7.1 Sender address rejected: not owned by user` error (the account used for setting up gmail is `admin.gmail@example.org` and `info.gmail@example.org` )
- Send some test emails to these addresses and make other tests. Then stop the container with `ctrl+c` and start it again as a daemon: `docker-compose up -d mail`.
- Now save on Moodle configuration the SMTP settings and test by trying to send some messages to other users:
If you are hiding your container behind a proxy service you might have discovered that the proxied requests from now on contain the proxy IP as the request origin. Whilst this behavior is technical correct it produces certain problems on the containers behind the proxy as they cannot distinguish the real origin of the requests anymore.
To solve this problem on TCP connections we can make use of the [proxy protocol](https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt). Compared to other workarounds that exist (`X-Forwarded-For` which only works for HTTP requests or `Tproxy` that requires you to recompile your kernel) the proxy protocol:
The configuration depends on the used proxy system. I will provide the configuration examples of [traefik v2](https://traefik.io/) using IMAP and SMTP with implicit TLS.
Keep in mind that it is neccessary to use port `10993` here. More information below at `dovecot` configuration.
### Configuration of the Backend (`dovecot` and `postfix`)
The following changes can be achived completely by adding the content to the appropriate files by using the projects [function to overwrite config files][docs-optionalconfig].
Port `10993` is used here to avoid conflicts with internal systems like `postscreen` and `amavis` as they will exchange messages on the default port and obviously have a different origin then compared to the proxy.