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hardware/mailserver

Build

Docker image

Simple and full-featured mail server as a set of multiple docker images includes :

  • Postfix : a full set smtp email server
  • Dovecot : secure imap and pop3 email server
  • Rspamd : anti-spam filter with SPF, DKIM, DMARC, ARC, ratelimit and greylisting capabilities
  • Clamav : antivirus with automatic updates
  • Zeyple : automatic GPG encryption of all your e-mails
  • Sieve : email filtering (vacation auto-responder, auto-forward...etc)
  • Fetchmail : fetch e-mails from external IMAP/POP3 server into local mailbox
  • Rainloop : web based email client
  • Postfixadmin : web based administration interface
  • Unbound: recursive caching DNS resolver with DNSSEC support
  • NSD : authoritative DNS server with DNSSEC support
  • Træfik : modern HTTP reverse proxy
  • SSL : lets encrypt with auto-renewal, custom and self-signed certificates support
  • Supporting multiple virtual domains over MySQL backend
  • Integration tests with Travis CI
  • Automated builds on DockerHub

System Requirements

Please check, if your system meets the following minimum system requirements :

Type Without ClamAV With ClamAV
CPU 1 GHz 1 GHz
RAM 1.5 GiB 2 GiB
Disk 5 GiB (without emails) 5 GiB (without emails)
System x86_64 x86_64

Prerequisites

Cleaning

Please remove any web server and mail services running on your server. I recommend using a clean installation of your prefered distro. If you are using Debian, remember to remove the default MTA Exim4 :

# apt-get purge exim4*

Also make sure that no other application is interfering with mail server configuration :

# netstat -tulpn | grep -E -w '25|80|110|143|443|465|587|993|995|4190'

If this command returns any results please remove or stop the application running on that port.

Ports

If you have a firewall, unblock the following ports, according to your needs :

Service Software Protocol Port
SMTP Postfix TCP 25
HTTP Nginx TCP 80
POP3 Dovecot TCP 110
IMAP Dovecot TCP 143
HTTPS Nginx TCP 443
SMTPS Postfix TCP 465
Submission Postfix TCP 587
IMAPS Dovecot TCP 993
POP3S Dovecot TCP 995
ManageSieve Dovecot TCP 4190

DNS setup

I recommend you to use hardware/nsd-dnssec as an authoritative name server with DNSSEC capabilities. NSD is an authoritative only, high performance, simple and open source name server.

Mandatory DNS records (A/MX) and reverse PTR :

A correct DNS setup is required, this step is very important.

HOSTNAME CLASS  TYPE PRIORITY VALUE
mail IN A/AAAA any 1.2.3.4
postfixadmin IN CNAME any mail.domain.tld.
spam IN CNAME any mail.domain.tld.
webmail IN CNAME any mail.domain.tld.
@ IN MX 10 mail.domain.tld.

Make sure that the PTR record of your IP matches the FQDN of your mailserver host. This record is usually set in your web hosting interface.

Recommended DNS records

DKIM, SPF and DMARC are recommended to build a good reputation score.

HOSTNAME CLASS  TYPE PRIORITY VALUE
@ IN TXT any "v=spf1 a mx ip4:SERVER_IPV4 ~all"
mail._domainkey IN TXT any "v=DKIM1; k=rsa; p=YOUR DKIM Public Key"
_dmarc IN TXT any "v=DMARC1; p=reject; rua=mailto:[email protected]; ruf=mailto:[email protected]; fo=0; adkim=s; aspf=s; pct=100; rf=afrf; sp=reject"

Note: The DKIM public key will be available on host after the container startup :

/mnt/docker/mail/dkim/domain.tld/public.key

These DNS record will raise your trust reputation score and reduce abuse of your domain name. You can find more information here :

Testing

You can audit your mailserver with the following assessment services :

Installation

1 - Prepare your environment

# Create a new docker network for Traefik
docker network create http_network

# Create the required folders and files
mkdir -p /mnt/docker/traefik/acme && cd /mnt/docker
touch docker-compose.yml traefik/traefik.toml traefik/acme/acme.json
chmod 600 docker-compose.yml traefik/traefik.toml traefik/acme/acme.json

2 - Get the latest docker-compose.yml and traefik.toml

Tags Description
1.1-stable Stable version (v1.1-stable branch)
1.1-latest Latest development build* (master branch)

*These builds have been validated through the CI automation system but they are not meant for deployment in production.

Don't forger to replace all values surrounded by {{ }} mark. Then, start all services :

docker-compose up -d

3 - Postfixadmin installation

PostfixAdmin is a web based interface used to manage mailboxes, virtual domains and aliases.

4 - Rainloop installation (optional)

Rainloop is a simple, modern and fast webmail with Sieve scripts support (filters and vacation message), GPG and a modern user interface.

5 - Done, congratulation ! 🎉

At first launch, the container takes few minutes to generate SSL certificates (if needed), DKIM keypair and update clamav database, all of this takes some time (1/2 minutes).

This image comes with a snake-oil self-signed certificate, please use your own trusted certificates. See below for configuration.

You can check the startup logs with this command :

# docker logs -f mailserver

[INFO] Let's encrypt live directory found
[INFO] Using /etc/letsencrypt/live/mail.domain.tld folder
[INFO] Creating DKIM keys for domain domain.tld
[INFO] Database hostname found in /etc/hosts
[INFO] Fetchmail forwarding is enabled.
[INFO] Automatic GPG encryption is enabled.
[INFO] ManageSieve protocol is enabled.
[INFO] POP3 protocol is enabled.
-------------------------------------------------------------------------------------
2017-08-26T11:06:58.885562+00:00 mail root: s6-supervise : spawning clamd process
2017-08-26T11:06:59.059077+00:00 mail root: s6-supervise : spawning freshclam process
2017-08-26T11:06:59.395214+00:00 mail root: s6-supervise : spawning rspamd process
2017-08-26T11:07:01.615597+00:00 mail root: s6-supervise : spawning unbound process
2017-08-26T11:07:01.870856+00:00 mail root: s6-supervise : spawning postfix process
2017-08-26T11:07:03.303536+00:00 mail root: s6-supervise : spawning dovecot process
...

Ansible Playbooks

logo

If you use Ansible, I recommend you to go to see @ksylvan playbooks here : https://github.com/ksylvan/docker-mail-server

Environment variables

⚠️ Use only ASCII printable characters in environment variables : https://en.wikipedia.org/wiki/ASCII#Printable_characters

Variable Description Type Default value
VMAILUID vmail user id optional 1024
VMAILGID vmail group id optional 1024
VMAIL_SUBDIR Individual mailbox' subdirectory optional mail
OPENDKIM_KEY_LENGTH Size of your DKIM RSA key pair optional 1024
PASSWORD_SCHEME Passwords encryption scheme optional SHA512-CRYPT
DBHOST MariaDB instance ip/hostname optional mariadb
DBPORT MariaDB instance port optional 3306
DBUSER MariaDB database username optional postfix
DBNAME MariaDB database name optional postfix
DBPASS MariaDB database password or location of a file containing it required null
REDIS_HOST Redis instance ip/hostname optional redis
REDIS_PORT Redis instance port optional 6379
REDIS_PASS Redis database password or location of a file containing it optional null
REDIS_NUMB Redis database number optional 0
RSPAMD_PASSWORD Rspamd WebUI and controller password or location of a file containing it required null
ADD_DOMAINS Add additional domains to the mailserver separated by commas (needed for dkim keys etc.) optional null
RELAY_NETWORKS Additional IPs or networks the mailserver relays without authentication optional null
DISABLE_RSPAMD_MODULE List of disabled modules separated by commas optional null
DISABLE_CLAMAV Disable virus scanning optional false
DISABLE_SIEVE Disable ManageSieve protocol optional false
DISABLE_SIGNING Disable DKIM/ARC signing optional false
DISABLE_GREYLISTING Disable greylisting policy optional false
DISABLE_RATELIMITING Disable ratelimiting policy optional false
DISABLE_DNS_RESOLVER Disable the local DNS resolver optional false
ENABLE_POP3 Enable POP3 protocol optional false
ENABLE_FETCHMAIL Enable fetchmail forwarding optional false
ENABLE_ENCRYPTION Enable automatic GPG encryption optional false
FETCHMAIL_INTERVAL Fetchmail polling interval optional 10
RECIPIENT_DELIMITER RFC 5233 subaddress extension separator (single character only) optional +
  • VMAIL_SUBDIR is the mail location subdirectory name /var/mail/vhosts/%domain/%user/$subdir. For more information, read this : https://wiki.dovecot.org/VirtualUsers/Home
  • PASSWORD_SCHEME for compatible schemes, read this : https://wiki.dovecot.org/Authentication/PasswordSchemes
  • Currently, only a single RECIPIENT_DELIMITER is supported. Support for multiple delimiters will arrive with Dovecot v2.3.
  • FETCHMAIL_INTERVAL must be a number between 1 and 59 minutes.
  • Use DISABLE_DNS_RESOLVER if you have some DNS troubles and DNSSEC lookup issues with the local DNS resolver.
  • Use DISABLE_RSPAMD_MODULE to disable any module listed here : https://rspamd.com/doc/modules/

Automatic GPG encryption of all your e-mails

How does it work ?

Zeyple catches email from the postfix queue, then encrypts it if a corresponding recipient's GPG public key is found. Finally, it puts it back into the queue.

zeyple

Enable automatic GPG encryption

❗ Please enable this option carefully and only if you know what you are doing.

Switch ENABLE_ENCRYPTION environment variable to true. The public keyring will be saved in /var/mail/zeyple/keys. Please don't change the default value of RECIPIENT_DELIMITER (default = "+"). If encryption is enabled with another delimiter, Zeyple could have an unpredictable behavior.

Import your public key

⚠️ Make sure to send your public key on a gpg keyserver before to run the following command.

docker exec -ti mailserver encryption.sh import-key YOUR_KEY_ID

Import all recipients public keys

This command browses all /var/mail/vhosts/* domains directories and users subdirectories to find all the recipients addresses in the mailserver.

docker exec -ti mailserver encryption.sh import-all-keys

Specify another gpg keyserver

docker exec -ti mailserver encryption.sh import-key YOUR_KEY_ID hkp://pgp.mit.edu
docker exec -ti mailserver encryption.sh import-all-keys hkp://keys.gnupg.net

Run other GPG options

You can use all options of gpg command line except an already assigned parameter called --homedir.

docker exec -ti mailserver encryption.sh --list-keys
docker exec -ti mailserver encryption.sh --fingerprint
docker exec -ti mailserver encryption.sh --refresh-keys
docker exec -ti mailserver encryption.sh ...

Documentation : https://www.gnupg.org/documentation/manuals/gnupg/Operational-GPG-Commands.html

Relaying from other networks

The RELAY_NETWORKS is a space separated list of additional IP addresses and subnets (in CIDR notation) which the mailserver relays without authentication. Hostnames are possible, but generally disadvised. IPv6 addresses must be surrounded by square brackets. You can also specify an absolut path to a file with IPs and networks so you can keep it on a mounted volume. Note that the file is not monitored for changes.

You can use this variable to allow other local containers to relay via the mailserver. Typically you would set this to the IP range of the default docker bridge (172.17.0.0/16) or the default network of your compose. If you are unable to determine, you might just add all RFC 1918 addresses 192.168.0.0/16 172.16.0.0/12 10.0.0.0/8

⚠️ A value like 0.0.0.0/0 will turn your mailserver into an open relay!

SSL certificates

01/20/2018 : For the moment, this docker image does not support Let's Encrypt certificates obtained automatically with Traefik, the acme.json storage support should arrive in the next few days.

You can use Let's Encrypt or any other certification authority. Setup your docker-compose.yml like this :

mailserver:
  image: hardware/mailserver
  volumes:
    - /mnt/docker/ssl:/etc/letsencrypt
    ...

Request your certificates in /mnt/docker/ssl/live/mail.domain.tld with an ACME client if you use Let's Encrypt, otherwise get your SSL certificates with the method provided by your CA and put everything needed in this directory.

Required files in this folder :

Filename Description
privkey.pem Private key for the certificate
cert.pem Server certificate only
chain.pem Root and intermediate certificates only, excluding server certificate
fullchain.pem All certificates, including server certificate. This is concatenation of cert.pem and chain.pem

Notes :

  • Important : When renewing certificates, you must restart the mailserver container.

  • If you do not use your own trusted certificates, a default self-signed certificate (RSA 4096 bits SHA2) is generated here : /mnt/docker/mail/ssl/selfsigned/{cert.pem, privkey.pem}.

  • If you have generated a ECDSA certificate with a curve other than prime256v1 (NIST P-256), you need to change the Postfix TLS configuration because of a change in OpenSSL >= 1.1.0. For example, if you use secp384r1 elliptic curve with your ECDSA certificate, change the tls_eecdh_strong_curve value :

# /mnt/docker/mail/postfix/custom.conf

tls_eecdh_strong_curve = secp384r1

Additional informations about this issue :

Testing

# IMAP STARTTLS - 143 port (IMAP)
openssl s_client -connect mail.domain.tld:143 -starttls imap -tlsextdebug

# SMTP STARTTLS - 587 port (Submission)
openssl s_client -connect mail.domain.tld:587 -starttls smtp -tlsextdebug

# IMAP SSL/TLS - 993 port (IMAPS)
openssl s_client -connect mail.domain.tld:993 -tlsextdebug

Unbound DNS resolver

Unbound is a validating, recursive, and caching DNS resolver inside the container, you can control it with the remote server control utility.

Some examples :

# Display server status
docker exec -ti mailserver unbound-control status

# Print server statistics
docker exec -ti mailserver unbound-control stats_noreset

# Reload the server. This flushes the cache and reads the config file.
docker exec -ti mailserver unbound-control reload

Documentation : https://www.unbound.net/documentation/unbound-control.html

Persistent files and folders in /mnt/docker/mail Docker volume

/mnt/docker
└──mail
   ├──postfix
   |     custom.conf
   |  ├──spool (Postfix queues directory)
   │  │     defer
   │  │     flush
   │  │     hold
   │  │     maildrop
   │  │     ...
   ├──dovecot
   |     instances
   |     ssl-parameters.dat
   |  ├──conf.d (Custom dovecot configuration)
   ├──clamav (ClamAV databases directory)
   │     bytecode.cvd
   │     daily.cld
   │     main.cvd
   ├──rspamd (Rspamd databases directory)
   │     rspamd.rrd
   |     stats.ucl
   ├──zeyple
   │  ├──keys (GPG public keyring)
   │  │     pubring.kbx
   │  │     trustdb.gpg
   │  │     ...
   ├──sieve
   │     default.sieve
   │     custom.sieve (custom default sieve rules for all users)
   ├──dkim
   │  ├──domain.tld
   │  │     private.key
   │  │     public.key
   ├──ssl
   │  ├──selfsigned (Auto-generated if no certificate found)
   │  │     cert.pem
   │  │     privkey.pem
   ├──vhosts
   │  ├──domain.tld
   │  │  ├──user
   │  │  │     .dovecot.sieve -> sieve/rainloop.user.sieve
   │  │  │     .dovecot.svbin
   │  │  │  ├──mail
   │  │  │  │  ├──.Archive
   │  │  │  │  ├──.Drafts
   │  │  │  │  ├──.Sent
   │  │  │  │  ├──.Spam
   │  │  │  │  ├──.Trash
   │  │  │  │  ├──cur
   │  │  │  │  ├──new
   │  │  │  │     ...
   │  │  │  ├──sieve
   │  │  │  │     rainloop.user.sieve (if using rainloop webmail)

Override postfix configuration

Postfix default configuration can be overrided providing a custom configuration file at postfix format. This can be used to also add configuration that are not in default configuration. Postfix documentation remains the best place to find configuration options.

Each line in the provided file will be loaded into Postfix. Create a new file here /mnt/docker/mail/postfix/custom.conf and add your custom options inside.

Example :

# /mnt/docker/mail/postfix/custom.conf

smtpd_banner = $myhostname ESMTP MyGreatMailServer
inet_protocols = ipv4
delay_notice_recipient = [email protected]
delay_warning_time = 2h
docker logs -f mailserver

[INFO] Override : smtpd_banner = $myhostname ESMTP MyGreatMailServer
[INFO] Override : inet_protocols = ipv4
[INFO] Override : delay_notice_recipient = [email protected]
[INFO] Override : delay_warning_time = 2h
[INFO] Custom Postfix configuration file loaded

Custom configuration for dovecot

Sometimes you might want to add additional configuration parameters or override the default ones. You can do so by placing configuration files to the persistent folder /mnt/docker/mail/dovecot/conf.d.

Example:

# /mnt/docker/mail/dovecot/conf.d/20-imap.conf

protocol imap {

  mail_max_userip_connections = 100

}

# /mnt/docker/mail/dovecot/conf.d/90-quota.conf

plugin {

  quota_rule2 = Trash:storage=+200M
  quota_exceeded_message = You have exceeded your mailbox quota.

}

Email client settings :

  • IMAP/SMTP username : [email protected]
  • Incoming IMAP server : mail.domain.tld (your FQDN)
  • Outgoing SMTP server : mail.domain.tld (your FQDN)
  • IMAP port : 993
  • SMTP port : 587
  • IMAP Encryption protocol : SSL/TLS
  • SMTP Encryption protocol : STARTTLS

Components

  • Postfix 3.1.4
  • Dovecot 2.2.27
  • Rspamd 1.6.5
  • Fetchmail 6.3.26
  • ClamAV 0.99.2
  • Zeyple 1.2.1
  • Unbound 1.6.0
  • s6 2.6.1.1
  • Rsyslog 8.24.0
  • ManageSieve server

Community projects

Some useful Thunderbird extensions :

Donation

My Bitcoin address : 1LwRr6jvzPHnZsxjk6u3wcfP555ZeC47Tg

This address is signed cryptographically to prove that it belongs to me. https://keybase.io/hardware

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🐳 Simple and full-featured mail server using Docker

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