## Building a simple mailserver
**WARNING**: 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](https://github.com/tomav/docker-mailserver/issues/1405#issuecomment-590106498) if IPv6 is enabled on the host machine but not in Docker. ([#1405](https://github.com/tomav/docker-mailserver/issues/1405))
We are going to use this docker based mailserver:
- First create a directory for the mailserver and get the setup script:
```
mkdir -p /var/ds/mail.example.org
cd /var/ds/mail.example.org/
curl -o setup.sh \
https://raw.githubusercontent.com/tomav/docker-mailserver/master/setup.sh
chmod a+x ./setup.sh
```
- Create the file `docker-compose.yml` with a content like this:
```
version: '2'
services:
mail:
image: tvial/docker-mailserver:latest
hostname: mail
domainname: example.org
container_name: mail
ports:
- "25:25"
- "587:587"
- "465:465"
volumes:
- ./data/:/var/mail/
- ./state/:/var/mail-state/
- ./config/:/tmp/docker-mailserver/
- /var/ds/wsproxy/letsencrypt/:/etc/letsencrypt/
environment:
- PERMIT_DOCKER=network
- SSL_TYPE=letsencrypt
- ONE_DIR=1
- DMS_DEBUG=1
- SPOOF_PROTECTION=0
- REPORT_RECIPIENT=1
- ENABLE_SPAMASSASSIN=0
- ENABLE_CLAMAV=0
- ENABLE_FAIL2BAN=1
- ENABLE_POSTGREY=0
cap_add:
- NET_ADMIN
- SYS_PTRACE
```
For more details about the environment variables that can be used,
and their meaning and possible values, check also these:
- https://github.com/tomav/docker-mailserver#environment-variables
- https://github.com/tomav/docker-mailserver/blob/master/.env.dist
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 these ports on the firewall: `25`, `587`, `465`
```
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`:
```
mail._domainkey IN TXT ( "v=DKIM1; h=sha256; k=rsa; "
"p=MIIBIjANBgkqhkiG9w0BAQEFACAQ8AMIIBCgKCAQEAaH5KuPYPSF3Ppkt466BDMAFGOA4mgqn4oPjZ5BbFlYA9l5jU3bgzRj3l6/Q1n5a9lQs5fNZ7A/HtY0aMvs3nGE4oi+LTejt1jblMhV/OfJyRCunQBIGp0s8G9kIUBzyKJpDayk2+KJSJt/lxL9Iiy0DE5hIv62ZPP6AaTdHBAsJosLFeAzuLFHQ6USyQRojefqFQtgYqWQ2JiZQ3"
"iqq3bD/BVlwKRp5gH6TEYEmx8EBJUuDxrJhkWRUk2VDl1fqhVBy8A9O7Ah+85nMrlOHIFsTaYo9o6+cDJ6t1i6G1gu+bZD0d3/3bqGLPBQV9LyEL1Rona5V7TJBGg099NQkTz1IwIDAQAB" ) ; ----- DKIM key mail for example.org
```
- Add these configurations as well on the same file on the DNS server:
```
mail IN A 10.11.12.13
; mailservers for example.org
3600 IN MX 1 mail.example.org.
; Add SPF record
IN TXT "v=spf1 mx ~all"
```
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:
```
cd /var/ds/wsproxy
ds domains-add mail mail.example.org
ds get-ssl-cert myemail@gmail.com mail.example.org --test
ds get-ssl-cert myemail@gmail.com mail.example.org
```
Now the certificates will be available on
`/var/ds/wsproxy/letsencrypt/live/mail.example.org`.
- Start the mailserver and check for any errors:
```
apt install docker-compose
docker-compose up mail
```
- Create email accounts and aliases with `SPOOF_PROTECTION=0`:
```
./setup.sh email add admin@example.org passwd123
./setup.sh email add info@example.org passwd123
./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.
- Or create email accounts and aliases with `SPOOF_PROTECTION=1`:
```
./setup.sh email add admin.gmail@example.org passwd123
./setup.sh email add info.gmail@example.org passwd123
./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:
- **SMTP hosts**: `mail.example.org:465`
- **SMTP security**: `SSL`
- **SMTP username**: `info@example.org`
- **SMTP password**: `passwd123`