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---
title: 'Tutorials | Installation Examples'
---
## 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 [if IPv6 is enabled on the host machine but not in Docker][github-issue-1405-comment].
We are going to use this docker based mailserver:
- First create a directory for the mailserver and get the setup script:
```sh
mkdir -p /var/ds/mail.example.org
cd /var/ds/mail.example.org/
curl -o setup.sh \
https://raw.githubusercontent.com/docker-mailserver/docker-mailserver/master/setup.sh
chmod a+x ./setup.sh
```
- Create the file `docker-compose.yml` with a content like this:
```yaml
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:
- [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; "
"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:
```txt
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:
```sh
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:
```sh
apt install docker-compose
docker-compose up mail
```
- Create email accounts and aliases with `SPOOF_PROTECTION=0`:
```sh
./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`:
```sh
./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`
[github-file-env]: https://github.com/docker-mailserver/docker-mailserver/blob/master/ENVIRONMENT.md
[github-file-dotenv]: https://github.com/docker-mailserver/docker-mailserver/blob/master/mailserver.env
[github-issue-1405-comment]: https://github.com/docker-mailserver/docker-mailserver/issues/1405#issuecomment-590106498

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## Using `docker-mailserver` behind a Proxy
### Information
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:
- It is protocol agnostic (can work with any layer 7 protocols, even when encrypted).
- It does not require any infrastructure changes.
- NAT-ing firewalls have no impact it.
- It is scalable.
There is only one condition: **both endpoints** of the connection MUST be compatible with proxy protocol.
Luckily `dovecot` and `postfix` are both Proxy-Protocol ready softwares so it depends only on your used reverse-proxy / loadbalancer.
### Configuration of the used Proxy Software
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.
Feel free to add your configuration if you achived the same goal using different proxy software below:
??? "Traefik v2"
Truncated configuration of traefik itself:
```yaml
version: '3.7'
services:
reverse-proxy:
image: traefik:v2.4
container_name: docker-traefik
restart: always
command:
- "--providers.docker"
- "--providers.docker.exposedbydefault=false"
- "--providers.docker.network=proxy"
- "--entrypoints.web.address=:80"
- "--entryPoints.websecure.address=:443"
- "--entryPoints.smtp.address=:25"
- "--entryPoints.smtp-ssl.address=:465"
- "--entryPoints.imap-ssl.address=:993"
- "--entryPoints.sieve.address=:4190"
ports:
- "25:25"
- "465:465"
- "993:993"
- "4190:4190"
[...]
```
Truncated list of neccessary labels on the mailserver container:
```yaml
version: '2'
services:
mail:
image: tvial/docker-mailserver:release-v7.2.0
restart: always
networks:
- proxy
labels:
- "traefik.enable=true"
- "traefik.tcp.routers.smtp.rule=HostSNI(`*`)"
- "traefik.tcp.routers.smtp.entrypoints=smtp"
- "traefik.tcp.routers.smtp.service=smtp"
- "traefik.tcp.services.smtp.loadbalancer.server.port=25"
- "traefik.tcp.services.smtp.loadbalancer.proxyProtocol.version=1"
- "traefik.tcp.routers.smtp-ssl.rule=HostSNI(`*`)"
- "traefik.tcp.routers.smtp-ssl.entrypoints=smtp-ssl"
- "traefik.tcp.routers.smtp-ssl.service=smtp-ssl"
- "traefik.tcp.services.smtp-ssl.loadbalancer.server.port=465"
- "traefik.tcp.services.smtp-ssl.loadbalancer.proxyProtocol.version=1"
- "traefik.tcp.routers.imap-ssl.rule=HostSNI(`*`)"
- "traefik.tcp.routers.imap-ssl.entrypoints=imap-ssl"
- "traefik.tcp.routers.imap-ssl.service=imap-ssl"
- "traefik.tcp.services.imap-ssl.loadbalancer.server.port=10993"
- "traefik.tcp.services.imap-ssl.loadbalancer.proxyProtocol.version=2"
- "traefik.tcp.routers.sieve.rule=HostSNI(`*`)"
- "traefik.tcp.routers.sieve.entrypoints=sieve"
- "traefik.tcp.routers.sieve.service=sieve"
- "traefik.tcp.services.sieve.loadbalancer.server.port=4190"
[...]
```
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].
Changes for `postfix` can be applied by adding the following content to `config/postfix-main.cf`:
```cf
postscreen_upstream_proxy_protocol = haproxy
```
and to `config/postfix-master.cf`:
```cf
submission/inet/smtpd_upstream_proxy_protocol=haproxy
smtps/inet/smtpd_upstream_proxy_protocol=haproxy
```
Changes for `dovecot` can be applied by adding the following content to `config/dovecot.cf`:
```cf
haproxy_trusted_networks = <your-proxy-ip>, <optional-cidr-notation>
haproxy_timeout = 3 secs
service imap-login {
inet_listener imaps {
haproxy = yes
ssl = yes
port = 10993
}
}
```
!!! note
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.
[docs-optionalconfig]: ../advanced/optional-config.md

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---
title: 'Use Cases | Forward-Only Mailserver with LDAP'
---
## Building a Forward-Only Mailserver
A **forward-only** mailserver does not have any local mailboxes. Instead, it has only aliases that forward emails to external email accounts (for example to a gmail account). You can also send email from the localhost (the computer where the mailserver is installed), using as sender any of the alias addresses.
The important settings for this setup (on `mailserver.env`) are these:
```env
PERMIT_DOCKER=host
ENABLE_POP3=
ENABLE_CLAMAV=0
SMTP_ONLY=1
ENABLE_SPAMASSASSIN=0
ENABLE_FETCHMAIL=0
```
Since there are no local mailboxes, we use `SMTP_ONLY=1` to disable `dovecot`. We disable as well the other services that are related to local mailboxes (`POP3`, `ClamAV`, `SpamAssassin`, etc.)
We can create aliases with `./setup.sh`, like this:
```sh
./setup.sh alias add <alias-address> <external-email-account>
```
## Authenticating with LDAP
If you want to send emails from outside the mailserver you have to authenticate somehow (with a username and password). One way of doing it is described in [this discussion][github-issue-1247]. However if there are many user accounts, it is better to use authentication with LDAP. The settings for this on `mailserver.env` are:
```env
ENABLE_LDAP=1
LDAP_START_TLS=yes
LDAP_SERVER_HOST=ldap.example.org
LDAP_SEARCH_BASE=ou=users,dc=example,dc=org
LDAP_BIND_DN=cn=mailserver,dc=example,dc=org
LDAP_BIND_PW=pass1234
ENABLE_SASLAUTHD=1
SASLAUTHD_MECHANISMS=ldap
SASLAUTHD_LDAP_SERVER=ldap.example.org
SASLAUTHD_LDAP_SSL=0
SASLAUTHD_LDAP_START_TLS=yes
SASLAUTHD_LDAP_BIND_DN=cn=mailserver,dc=example,dc=org
SASLAUTHD_LDAP_PASSWORD=pass1234
SASLAUTHD_LDAP_SEARCH_BASE=ou=users,dc=example,dc=org
SASLAUTHD_LDAP_FILTER=(&(uid=%U)(objectClass=inetOrgPerson))
```
My LDAP data structure is very basic, containing only the username, password, and the external email address where to forward emails for this user. An entry looks like this
```properties
add uid=username,ou=users,dc=example,dc=org
uid: username
objectClass: inetOrgPerson
sn: username
cn: username
userPassword: {SSHA}abcdefghi123456789
email: real-email-address@external-domain.com
```
This structure is different from what is expected/assumed from the configuration scripts of the mailserver, so it doesn't work just by using the `LDAP_QUERY_FILTER_...` settings. Instead, I had to do [custom configuration][github-file-readme-patches]. I created the script `config/user-patches.sh`, with a content like this:
```bash
#!/bin/bash
rm -f /etc/postfix/{ldap-groups.cf,ldap-domains.cf}
postconf \
"virtual_mailbox_domains = /etc/postfix/vhost" \
"virtual_alias_maps = ldap:/etc/postfix/ldap-aliases.cf texthash:/etc/postfix/virtual" \
"smtpd_sender_login_maps = ldap:/etc/postfix/ldap-users.cf"
sed -i /etc/postfix/ldap-users.cf \
-e '/query_filter/d' \
-e '/result_attribute/d' \
-e '/result_format/d'
cat <<EOF >> /etc/postfix/ldap-users.cf
query_filter = (uid=%u)
result_attribute = uid
result_format = %s@example.org
EOF
sed -i /etc/postfix/ldap-aliases.cf \
-e '/domain/d' \
-e '/query_filter/d' \
-e '/result_attribute/d'
cat <<EOF >> /etc/postfix/ldap-aliases.cf
domain = example.org
query_filter = (uid=%u)
result_attribute = mail
EOF
postfix reload
```
You see that besides `query_filter`, I had to customize as well `result_attribute` and `result_format`.
For more details about using LDAP see: [LDAP managed mail server with Postfix and Dovecot for multiple domains](https://www.vennedey.net/resources/2-LDAP-managed-mail-server-with-Postfix-and-Dovecot-for-multiple-domains)
Another solution that serves as a forward-only mailserver is this: https://gitlab.com/docker-scripts/postfix
[github-file-readme-patches]: https://github.com/docker-mailserver/docker-mailserver/blob/master/README.md#custom-user-changes--patches
[github-issue-1247]: https://github.com/docker-mailserver/docker-mailserver/issues/1247