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FAQ

What kind of database are you using?

None! No database is required. The filesystem is the database. This image is based on config files that can be persisted using bind mounts (default) or Docker volumes, and as such versioned, backed up and so forth.

Where are emails stored?

Mails are stored in /var/mail/${domain}/${username}. Since v9.0.0 it is possible to add custom user_attributes for each accounts to have a different mailbox configuration (See #1792).

How are IMAP mailboxes (aka IMAP Folders) set up?

INBOX is setup by default with the special IMAP folders Drafts, Sent, Junk and Trash. You can learn how to modify or add your own folders (including additional special folders like Archive) by visiting our docs page Customizing IMAP Folders for more information.

How do I update DMS?

Make sure to read the CHANGELOG before updating to new versions, to be prepared for possible breaking changes.

Then, run the following commands:

docker-compose pull
docker-compose down
docker-compose up -d

You should see the new version number on startup, for example: [ INF ] Welcome to docker-mailserver 11.3.1. And you're done! Don't forget to have a look at the remaining functions of the setup.sh script with ./setup.sh help.

Which operating systems are supported?

  • Linux is officially supported.
  • Windows and macOS are not supported and users and have reported various issues running the image on these hosts.

As you'll realistically be deploying to production on a Linux host, if you are on Windows or macOS and want to run the image locally first, it's advised to do so via a VM guest running Linux if you have issues running DMS on your host system.

What are the system requirements?

  • 1 vCore
  • 2GB RAM
  • Swap enabled for the container

Minimum

  • 1 vCore
  • 512MB RAM
  • You'll need to avoid running some services like ClamAV (disabled by default) to be able to run on a host with 512MB of RAM.

Warning

ClamAV can consume a lot of memory, as it reads the entire signature database into RAM.

Current figure is about 850M and growing. If you get errors about ClamAV or amavis failing to allocate memory you need more RAM or more swap and of course docker must be allowed to use swap (not always the case). If you can't use swap at all you may need 3G RAM.

How to alter a running DMS instance without relaunching the container?

docker-mailserver aggregates multiple "sub-services", such as Postfix, Dovecot, Fail2ban, SpamAssassin, etc. In many cases, one may edit a sub-service's config and reload that very sub-service, without stopping and relaunching the whole mail-server.

In order to do so, you'll probably want to push your config updates to your server through a Docker volume (these docs use: ./docker-data/dms/config/:/tmp/docker-mailserver/), then restart the sub-service to apply your changes, using supervisorctl. For instance, after editing fail2ban's config: supervisorctl restart fail2ban.

See the documentation for supervisorctl.

Tip

To add, update or delete an email account; there is no need to restart postfix / dovecot service inside the container after using setup.sh script.

For more information, see #1639.

How can I sync the container and host date/time?

Share the host's /etc/localtime with the container, e.g. by using a bind mount:

volumes:
  - /etc/localtime:/etc/localtime:ro

Optionally, you can set the TZ ENV variable; e.g. TZ=Europe/Berlin. Check this list for which values are allowed.

What is the file format?

All files are using the Unix format with LF line endings. Please do not use CRLF.

Do you support multiple domains?

DMS supports multiple domains out of the box, so you can do this:

./setup.sh email add user1@example.com
./setup.sh email add user1@example.de
./setup.sh email add user1@server.example.org

What about backups?

Bind mounts (default)

From the location of your docker-compose.yml, create a compressed archive of your docker-data/dms/config/ and docker-data/dms/mail-* folders:

tar --gzip -cf "backup-$(date +%F).tar.gz" ./docker-data/dms

Then to restore docker-data/dms/config/ and docker-data/dms/mail-* folders from your backup file:

tar --gzip -xf backup-date.tar.gz

Volumes

Assuming that you use docker-compose and data volumes, you can backup the configuration, emails and logs like this:

# create backup
docker run --rm -it \
  -v "${PWD}/docker-data/dms/config/:/tmp/docker-mailserver/" \
  -v "${PWD}/docker-data/dms-backups/:/backup/" \
  --volumes-from mailserver \
  alpine:latest \
  tar czf "/backup/mail-$(date +%F).tar.gz" /var/mail /var/mail-state /var/log/mail /tmp/docker-mailserver

# delete backups older than 30 days
find "${PWD}/docker-data/dms-backups/" -type f -mtime +30 -delete

What about the ./docker-data/dms/mail-state folder?

When you run DMS with the ENV variable ONE_DIR=1 (default), this folder will:

  • Provide support to persist Fail2Ban blocks, ClamAV signature updates, and the like when the container is restarted or recreated.
  • To persist that container state properly this folder should be volume mounted to /var/mail-state/ internally.

Service data is relocated to the mail-state folder for the following services: Postfix, Dovecot, Fail2Ban, Amavis, PostGrey, ClamAV, SpamAssassin.

I Want to Know More About the Ports

See this part of the documentation for further details and best practice advice, especially regarding security concerns.

How can I configure my email client?

Login is full email address (<user>@<domain>).

# IMAP
username:           <user1@example.com>
password:           <mypassword>
server:             <mail.example.com>
imap port:          143 or 993 with STARTTLS/SSL (recommended)
imap path prefix:   INBOX

# SMTP
smtp port:          25 or 587/465 with STARTTLS/SSL (recommended)
username:           <user1@example.com>
password:           <mypassword>

DMS is properly configured for port 587, if possible, we recommend using port 465 for SMTP though. See this section to learn more about ports.

Can I use a naked/bare domain (i.e. no hostname)?

Yes, but not without some configuration changes. Normally it is assumed that DMS runs on a host with a name, so the fully qualified host name might be mail.example.com with the domain example.com. The MX records point to mail.example.com.

To use a bare domain (where the host name is example.com and the domain is also example.com), change mydestination:

  • From: mydestination = $myhostname, localhost.$mydomain, localhost
  • To: mydestination = localhost.$mydomain, localhost

Add the latter line to docker-data/dms/config/postfix-main.cf. If that doesn't work, make sure that OVERRIDE_HOSTNAME is blank in your mailserver.env file (see #1731). Without these changes there will be warnings in the logs like:

warning: do not list domain example.com in BOTH mydestination and virtual_mailbox_domains

Plus of course mail delivery fails.

Also you need to define hostname: example.com in your docker-compose.yml and don't sepecify the domainname: at all.

How can I configure a catch-all?

Considering you want to redirect all incoming e-mails for the domain example.com to user1@example.com, add the following line to docker-data/dms/config/postfix-virtual.cf:

@example.com user1@example.com

How can I delete all the emails for a specific user?

First of all, create a special alias named devnull by editing docker-data/dms/config/postfix-aliases.cf:

devnull: /dev/null

Considering you want to delete all the e-mails received for baduser@example.com, add the following line to docker-data/dms/config/postfix-virtual.cf:

baduser@example.com devnull

Important

If you use a catch-all rule for the main/sub domain, you need another entry in docker-data/dms/config/postfix-virtual.cf:

@mail.example.com hello@example.com
baduser@example.com devnull
devnull@mail.example.com devnull

What kind of SSL certificates can I use?

Both RSA and ECDSA certs are supported. You can provide your own cert files manually, or mount a letsencrypt generated directory (with alternative support for Traefik's acme.json). Check out the SSL_TYPE documentation for more details.

I just moved from my old mail server to DMS, but "it doesn't work"?

If this migration implies a DNS modification, be sure to wait for DNS propagation before opening an issue. Few examples of symptoms can be found here or here.

This could be related to a modification of your MX record, or the IP mapped to mail.example.com. Additionally, validate your DNS configuration.

If everything is OK regarding DNS, please provide formatted logs and config files. This will allow us to help you.

If we're blind, we won't be able to do anything.

Can DMS run in a Rancher environment?

Yes, by adding the environment variable PERMIT_DOCKER: network.

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, for instance if IPv6 is enabled on the host machine but not in Docker.

How can I authenticate users with SMTP_ONLY=1?

See #1247 for an example.

Todo

Write a How-to / Use-Case / Tutorial about authentication with SMTP_ONLY.

Common Errors

warning: connect to Milter service inet:localhost:8893: Connection refused
# DMARC not running
# => /etc/init.d/opendmarc restart

warning: connect to Milter service inet:localhost:8891: Connection refused
# DKIM not running
# => /etc/init.d/opendkim restart

mail amavis[1459]: (01459-01) (!)connect to /var/run/clamav/clamd.ctl failed, attempt #1: Can't connect to a UNIX socket /var/run/clamav/clamd.ctl: No such file or directory
mail amavis[1459]: (01459-01) (!)ClamAV-clamd: All attempts (1) failed connecting to /var/run/clamav/clamd.ctl, retrying (2)
mail amavis[1459]: (01459-01) (!)ClamAV-clamscan av-scanner FAILED: /usr/bin/clamscan KILLED, signal 9 (0009) at (eval 100) line 905.
mail amavis[1459]: (01459-01) (!!)AV: ALL VIRUS SCANNERS FAILED
# Clamav is not running (not started or because you don't have enough memory)
# => check requirements and/or start Clamav

How to use DMS behind a proxy

Using user-patches.sh, update the container file /etc/postfix/main.cf to include:

proxy_interfaces = X.X.X.X (your public IP)

How to adjust settings with the user-patches.sh script

Suppose you want to change a number of settings that are not listed as variables or add things to the server that are not included?

docker-mailserver has a built-in way to do post-install processes. If you place a script called user-patches.sh in the config directory it will be run after all configuration files are set up, but before the postfix, amavis and other daemons are started.

It is common to use a local directory for config added to docker-mailsever via a volume mount in your docker-compose.yml (eg: ./docker-data/dms/config/:/tmp/docker-mailserver/).

Add or create the script file to your config directory:

cd ./docker-data/dms/config
touch user-patches.sh
chmod +x user-patches.sh

Then fill user-patches.sh with suitable code.

If you want to test it you can move into the running container, run it and see if it does what you want. For instance:

# start shell in container
./setup.sh debug login

# check the file
cat /tmp/docker-mailserver/user-patches.sh

# run the script
/tmp/docker-mailserver/user-patches.sh

# exit the container shell back to the host shell
exit

You can do a lot of things with such a script. You can find an example user-patches.sh script here: example user-patches.sh script.

We also have a very similar docs page specifically about this feature!

Special use-case - patching the supervisord configuration

It seems worth noting, that the user-patches.sh gets executed through supervisord. If you need to patch some supervisord config (e.g. /etc/supervisor/conf.d/saslauth.conf), the patching happens too late.

An easy workaround is to make the user-patches.sh reload the supervisord config after patching it:

#!/bin/bash
sed -i 's/rimap -r/rimap/' /etc/supervisor/conf.d/saslauth.conf
supervisorctl update

How to ban custom IP addresses with Fail2ban

Use the following command:

./setup.sh fail2ban ban <IP>

The default bantime is 180 days. This value can be customized.

What to do in case of SPF/Forwarding problems

If you got any problems with SPF and/or forwarding mails, give SRS a try. You enable SRS by setting ENABLE_SRS=1. See the variable description for further information.

Why are my emails not being delivered?

There are many reasons why email might be rejected, common causes are:

  • Wrong or untrustworthy SSL certificate.
  • A TLD (your domain) or IP address with a bad reputation.
  • Misconfigured DNS records.

DMS does not manage those concerns, verify they are not causing your delivery problems before reporting a bug on our issue tracker. Resources that can help you troubleshoot:

  • mail-tester can test your deliverability.
  • helloinbox provides a checklist of things to improve your deliverability.

SpamAssasin

How can I manage my custom SpamAssassin rules?

Antispam rules are managed in docker-data/dms/config/spamassassin-rules.cf.

What are acceptable SA_SPAM_SUBJECT values?

For no subject set SA_SPAM_SUBJECT=undef.

For a trailing white-space subject one can define the whole variable with quotes in docker-compose.yml:

environment:
  - "SA_SPAM_SUBJECT=[SPAM] "

Why are SpamAssassin x-headers not inserted into my subdomain.example.com subdomain emails?

In the default setup, amavis only applies SpamAssassin x-headers into domains matching the template listed in the config file (05-domain_id in the amavis defaults).

The default setup @local_domains_acl = ( ".$mydomain" ); does not match subdomains. To match subdomains, you can override the @local_domains_acl directive in the amavis user config file 50-user with @local_domains_maps = ("."); to match any sort of domain template.

How can I make SpamAssassin better recognize spam?

Put received spams in .Junk/ imap folder using SPAMASSASSIN_SPAM_TO_INBOX=1 and MOVE_SPAM_TO_JUNK=1 and add a user cron like the following:

# This assumes you're having `environment: ONE_DIR=1` in the `mailserver.env`,
# with a consolidated config in `/var/mail-state`
#
# m h dom mon dow command
# Everyday 2:00AM, learn spam from a specific user
0 2 * * * docker exec mailserver sa-learn --spam /var/mail/example.com/username/.Junk --dbpath /var/mail-state/lib-amavis/.spamassassin

With docker-compose you can more easily use the internal instance of cron within docker-mailserver. This is less problematic than the simple solution shown above, because it decouples the learning from the host on which docker-mailserver is running, and avoids errors if the mail-server is not running.

The following configuration works nicely:

Example

Create a system cron file:

# in the docker-compose.yml root directory
mkdir -p ./docker-data/dms/cron
touch ./docker-data/dms/cron/sa-learn
chown root:root ./docker-data/dms/cron/sa-learn
chmod 0644 ./docker-data/dms/cron/sa-learn

Edit the system cron file nano ./docker-data/dms/cron/sa-learn, and set an appropriate configuration:

# This assumes you're having `environment: ONE_DIR=1` in the env-mailserver,
# with a consolidated config in `/var/mail-state`
#
# '> /dev/null' to send error notifications from 'stderr' to 'postmaster@example.com'
#
# m h dom mon dow user command
#
# Everyday 2:00AM, learn spam from a specific user
# spam: junk directory
0  2 * * * root  sa-learn --spam /var/mail/example.com/username/.Junk --dbpath /var/mail-state/lib-amavis/.spamassassin > /dev/null
# ham: archive directories
15 2 * * * root  sa-learn --ham /var/mail/example.com/username/.Archive* --dbpath /var/mail-state/lib-amavis/.spamassassin > /dev/null
# ham: inbox subdirectories
30 2 * * * root  sa-learn --ham /var/mail/example.com/username/cur* --dbpath /var/mail-state/lib-amavis/.spamassassin > /dev/null
#
# Everyday 3:00AM, learn spam from all users of a domain
# spam: junk directory
0  3 * * * root  sa-learn --spam /var/mail/not-example.com/*/.Junk --dbpath /var/mail-state/lib-amavis/.spamassassin > /dev/null
# ham: archive directories
15 3 * * * root  sa-learn --ham /var/mail/not-example.com/*/.Archive* --dbpath /var/mail-state/lib-amavis/.spamassassin > /dev/null
# ham: inbox subdirectories
30 3 * * * root  sa-learn --ham /var/mail/not-example.com/*/cur* --dbpath /var/mail-state/lib-amavis/.spamassassin > /dev/null

Then with docker-compose.yml:

services:
  mailserver:
    image: docker.io/mailserver/docker-mailserver:latest
    volumes:
      - ./docker-data/dms/cron/sa-learn:/etc/cron.d/sa-learn

Or with Docker Swarm:

version: '3.8'

services:
  mailserver:
    image: docker.io/mailserver/docker-mailserver:latest
    # ...
    configs:
      - source: my_sa_crontab
        target: /etc/cron.d/sa-learn

configs:
  my_sa_crontab:
    file: ./docker-data/dms/cron/sa-learn

With the default settings, SpamAssassin will require 200 mails trained for spam (for example with the method explained above) and 200 mails trained for ham (using the same command as above but using --ham and providing it with some ham mails). Until you provided these 200+200 mails, SpamAssassin will not take the learned mails into account. For further reference, see the SpamAssassin Wiki.

How do I have more control about what SpamAssassin is filtering?

By default, SPAM and INFECTED emails are put to a quarantine which is not very straight forward to access. Several config settings are affecting this behavior:

First, make sure you have the proper thresholds set:

SA_TAG=-100000.0
SA_TAG2=3.75
SA_KILL=100000.0
  • The very negative vaue in SA_TAG makes sure, that all emails have the SpamAssassin headers included.
  • SA_TAG2 is the actual threshold to set the YES/NO flag for spam detection.
  • SA_KILL needs to be very high, to make sure nothing is bounced at all (SA_KILL superseeds SPAMASSASSIN_SPAM_TO_INBOX)

Make sure everything (including SPAM) is delivered to the inbox and not quarantined:

SPAMASSASSIN_SPAM_TO_INBOX=1

Use MOVE_SPAM_TO_JUNK=1 or create a sieve script which puts spam to the Junk folder:

require ["comparator-i;ascii-numeric","relational","fileinto"];

if header :contains "X-Spam-Flag" "YES" {
  fileinto "Junk";
} elsif allof (
   not header :matches "x-spam-score" "-*",
   header :value "ge" :comparator "i;ascii-numeric" "x-spam-score" "3.75" ) {
  fileinto "Junk";
}

Create a dedicated mailbox for emails which are infected/bad header and everything amavis is blocking by default and put its address into docker-data/dms/config/amavis.cf

$clean_quarantine_to      = "amavis\@example.com";
$virus_quarantine_to      = "amavis\@example.com";
$banned_quarantine_to     = "amavis\@example.com";
$bad_header_quarantine_to = "amavis\@example.com";
$spam_quarantine_to       = "amavis\@example.com";