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Prepare Your System

Before you run mailcow: dockerized, there are a few requirements that you should check:


When running mailcow: dockerized on a Debian 8 (Jessie) box, you should switch to kernel 4.9 from Jessie backports to avoid a bug when running Docker containers with healthchecks! For more details read:


  • mailcow: dockerized requires some ports to be open for incoming connections, so make sure that your firewall is not blocking these.
  • Make sure that no other application is interfering with mailcow's configuration, such as another mail service
  • A correct DNS setup is crucial to every good mailserver setup, so please make sure you got at least the basics covered before you begin!
  • Make sure that your system has a correct date and time setup. This is crucial for stuff like two factor TOTP authentication.

Minimum System Resources

Please make sure that your system has at least the following resources:

Resource mailcow: dockerized
RAM                     1 GiB (or better 1,5 GiB + Swap)
Disk 5 GiB (without emails)
System Type x86_64

ClamAV is a greedy RAM muncher. You can disable it in mailcow.conf by settings SKIP_CLAMD=y.

Firewall & Ports

Please check if any of mailcow's standard ports are open and not in use by other applications:

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

If this command returns any results please remove or stop the application running on that port. You may also adjust mailcows ports via the mailcow.conf configuration file.

Default Ports

If you have a firewall already up and running please make sure that these ports are open for incoming connections:

Service Protocol Port Container Variable
Postfix SMTP TCP 25 postfix-mailcow ${SMTP_PORT}
Postfix SMTPS TCP 465 postfix-mailcow ${SMTPS_PORT}
Postfix Submission TCP 587 postfix-mailcow ${SUBMISSION_PORT}
Dovecot IMAP TCP 143 dovecot-mailcow ${IMAP_PORT}
Dovecot IMAPS TCP 993 dovecot-mailcow ${IMAPS_PORT}
Dovecot POP3 TCP 110 dovecot-mailcow ${POP_PORT}
Dovecot POP3S TCP 995 dovecot-mailcow ${POPS_PORT}
Dovecot ManageSieve TCP 4190 dovecot-mailcow ${SIEVE_PORT}
HTTP(S) TCP 80/443 nginx-mailcow ${HTTP_PORT} / ${HTTPS_PORT}

To bind a service to an IP address, you can prepend the IP like this: SMTP_PORT=

Important: You cannot use IP:PORT bindings in HTTP_PORT and HTTPS_PORT. Please use HTTP_PORT=1234 and HTTP_BIND= instead.

To unblock firewalls using ufw you can use the following commands:

# ufw allow 25
# ufw allow 80
# ufw allow 110
# ufw allow 143
# ufw allow 443
# ufw allow 465
# ufw allow 587
# ufw allow 993
# ufw allow 995

Date and Time

To ensure that you have the correct date and time setup on your system, please check the output of timedatectl status:

$ timedatectl status
      Local time: Sat 2017-05-06 02:12:33 CEST
  Universal time: Sat 2017-05-06 00:12:33 UTC
        RTC time: Sat 2017-05-06 00:12:32
       Time zone: Europe/Berlin (CEST, +0200)
     NTP enabled: yes
NTP synchronized: yes
 RTC in local TZ: no
      DST active: yes
 Last DST change: DST began at
                  Sun 2017-03-26 01:59:59 CET
                  Sun 2017-03-26 03:00:00 CEST
 Next DST change: DST ends (the clock jumps one hour backwards) at
                  Sun 2017-10-29 02:59:59 CEST
                  Sun 2017-10-29 02:00:00 CET

The lines NTP enabled: yes and NTP synchronized: yes indicate wether you have NTP enabled and if it's synchronized.

To enable NTP you need to run the command timedatectl set-ntp true. You also need to edit your /etc/systemd/timesyncd.conf:

# vim /etc/systemd/timesyncd.conf