First Steps

SSL (and: How to use Let's Encrypt)

mailcow dockerized comes with a snakeoil CA "mailcow" and a server certificate in data/assets/ssl. Please use your own trusted certificates.

mailcow uses 3 domain names that should be covered by your new certificate:

  • autodiscover.example.org
  • autoconfig.example.org

Obtain multi-SAN certificate by Let's Encrypt

This is just an example of how to obtain certificates with certbot. There are several methods!

1. Get the certbot client:

wget https://dl.eff.org/certbot-auto -O /usr/local/sbin/certbot && chmod +x /usr/local/sbin/certbot

2. Make sure you set HTTP_BIND= and HTTP_PORT=80 in mailcow.conf or setup a reverse proxy to enable connections to port 80. If you changed HTTP_BIND, then restart Nginx:

docker-compose restart nginx-mailcow

3. Request the certificate with the webroot method:

cd /path/to/git/clone/mailcow-dockerized
source mailcow.conf
certbot certonly \
    --webroot \
    -w ${PWD}/data/web \
    -d autodiscover.example.org \
    -d autoconfig.example.org \
    --email you@example.org \

4. Create hard links to the full path of the new certificates. Assuming you are still in the mailcow root folder:

mv data/assets/ssl/cert.{pem,pem.backup}
mv data/assets/ssl/key.{pem,pem.backup}
ln $(readlink -f /etc/letsencrypt/live/${MAILCOW_HOSTNAME}/fullchain.pem) data/assets/ssl/cert.pem
ln $(readlink -f /etc/letsencrypt/live/${MAILCOW_HOSTNAME}/privkey.pem) data/assets/ssl/key.pem

5. Restart affected containers:

docker-compose restart postfix-mailcow dovecot-mailcow nginx-mailcow

When renewing certificates, run the last two steps (link + restart) as post-hook in a script.

Rspamd Web UI

At first you may want to setup Rspamds web interface which provides some useful features and information.

1. Generate a Rspamd controller password hash:

docker-compose exec rspamd-mailcow rspamadm pw

2. Replace the default hash in data/conf/rspamd/override.d/worker-controller.inc by your newly generated:

enable_password = "myhash";

You can use password = "myhash"; instead of enable_password to disable write-access in the web UI.

3. Restart rspamd:

docker-compose restart rspamd-mailcow

Open https://${MAILCOW_HOSTNAME}/rspamd in a browser and login!

Optional: Reverse proxy

You don't need to change the Nginx site that comes with mailcow: dockerized. mailcow: dockerized trusts the default gateway IP as proxy. This is very important to control access to Rspamd's web UI.

1. Make sure you change HTTP_BIND and HTTPS_BIND in mailcow.conf to a local address and set the ports accordingly, for example:


IMPORTANT: Do not use port 8081

Recreate affected containers by running docker-compose up -d.

2. Configure your local webserver as reverse proxy:

Apache 2.4

<VirtualHost *:443>
    ServerName mail.example.org
    ServerAlias autodiscover.example.org
    ServerAlias autoconfig.example.org

    # You should proxy to a plain HTTP session to offload SSL processing
    ProxyPass /
    ProxyPassReverse /
    ProxyPreserveHost Off

    # If you plan to proxy to a HTTPS host:
    #SSLProxyEngine On

    # If you plan to proxy to an untrusted HTTPS host:
    #SSLProxyVerify none
    #SSLProxyCheckPeerCN off
    #SSLProxyCheckPeerName off
    #SSLProxyCheckPeerExpire off


server {
    listen 443;
    server_name mail.example.org autodiscover.example.org autoconfig.example.org;

    location / {
        proxy_redirect $scheme://$host:$server_port/;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;

Optional: Setup a relayhost

Insert these lines to data/conf/postfix/main.cf. "relayhost" does already exist (empty), just change its value.

relayhost = [your-relayhost]:587
smtp_sasl_password_maps = hash:/opt/postfix/conf/smarthost_passwd
smtp_sasl_auth_enable = yes

Create the credentials file:

echo "your-relayhost username:password" > data/conf/postfix/smarthost_passwd


docker-compose exec postfix-mailcow postmap /opt/postfix/conf/smarthost_passwd
docker-compose exec postfix-mailcow chown root:postfix /opt/postfix/conf/smarthost_passwd /opt/postfix/conf/smarthost_passwd.db
docker-compose exec postfix-mailcow chmod 660 /opt/postfix/conf/smarthost_passwd /opt/postfix/conf/smarthost_passwd.db
docker-compose exec postfix-mailcow postfix reload

Optional: Log to Syslog

Enable Rsyslog to receive logs on 524/tcp:

# This setting depends on your Rsyslog version and configuration format.
# For most Debian derivates it will work like this...
$ModLoad imtcp
$InputTCPServerRun 524

# ...while for Ubuntu 16.04 it looks like this:
input(type="imtcp" address="" port="524")

# No matter your Rsyslog version, you should set this option to off
# if you plan to use Fail2ban
$RepeatedMsgReduction off

Restart rsyslog after enabling the TCP listener.

Now setup Docker daemon to start with the syslog driver. This enables the syslog driver for all containers!

Debian users can change the startup configuration in /etc/default/docker while CentOS users find it in /etc/sysconfig/docker:

DOCKER_OPTS="--log-driver=syslog --log-opt syslog-address=tcp://"

Caution: For some reason Ubuntu 16.04 and some, but not all, systemd based distros do not read the defaults file parameters.

Just run systemctl edit docker.service and add the following content to fix it.

Note: If "systemctl edit" is not available, just copy the content to /etc/systemd/system/docker.service.d/override.conf.

The first empty ExecStart parameter is not a mistake.

ExecStart=/usr/bin/docker daemon -H fd:// $DOCKER_OPTS

Restart the Docker daemon and run docker-compose down && docker-compose up -d to recreate the containers.

Use Fail2ban

This is a subsection of "Log to Syslog", which is required for Fail2ban to work.

Open /etc/fail2ban/filter.d/common.conf and search for the prefix_line parameter, change it to ".*":

__prefix_line = .*

Create /etc/fail2ban/jail.d/dovecot.conf...

enabled = true
filter  = dovecot
logpath = /var/log/syslog
chain = FORWARD

and jail.d/postfix-sasl.conf:

enabled = true
filter  = postfix-sasl
logpath = /var/log/syslog
chain = FORWARD

Restart Fail2ban.

Install a local MTA

The easiest option would be to disable the listener on port 25/tcp.

Postfix users disable the listener by commenting the following line (starting with smtp or 25) in /etc/postfix/master.cf:

#smtp      inet  n       -       -       -       -       smtpd

Restart Postfix after applying your changes.

Sender and receiver model

When a mailbox is created, a user is allowed to send mail from and receive mail for his own mailbox address.

Mailbox me@example.org is created. example.org is a primary domain. 
Note: a mailbox cannot be created in an alias domain.

me@example.org is only known as me@example.org.
me@example.org is allowed to send as me@example.org.

We can add an alias domain for example.org:

Alias domain alias.com is added and assigned to primary domain example.org.
me@example.org is now known as me@example.org and me@alias.com.
me@example.org is now allowed to send as me@example.org and me@alias.com.

We can add aliases for a mailbox to receive mail for and to send from this new address.

It is important to know, that you are not able to receive mail for my-alias@my-alias-domain.tld. You would need to create this particular alias.

me@example.org is assigned the alias alias@example.org
me@example.org is now known as alias@example.org, me@alias.com, alias@example.org

me@example.org is NOT known as alias@alias.com.

Administrators and domain administrators can edit mailboxes to allow specific users to send as other mailbox users ("delegate" them).

You can choose between mailbox users or completely disable the sender check for domains.

SOGo "mail from" addresses

Mailbox users can, obviously, select their own mailbox address, as well as all alias addresses and aliases that exist through alias domains.

If you want to select another existing mailbox user as your "mail from" address, this user has to delegate you access through SOGo (see SOGo documentation). Moreover a mailcow (domain) administrator needs to grant you access as described above.