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Configuration reference

This page explains the variables found in mailu.env. In most cases mailu.env is setup correctly by the setup utility and can be left as-is. However, some advanced settings or modifications can be done by modifying this file.

Common configuration

The SECRET_KEY must be changed for every setup and set to a 16 bytes randomly generated value. It is intended to secure authentication cookies among other critical uses. This can be generated with a utility such as pwgen, which can be installed on most Linux systems:

apt-get install pwgen
pwgen 16 1

The DOMAIN holds the main e-mail domain for the server. This email domain is used for bounce emails, for generating the postmaster email and other technical addresses.

The HOSTNAMES are all public hostnames for the mail server. Mailu supports a mail server with multiple hostnames. The first declared hostname is the main hostname and will be exposed over SMTP, IMAP, etc.

The SUBNET defines the address range of the docker network used by Mailu. This should not conflict with any networks to which your system is connected. (Internal and external!). Normally this does not need to be changed, unless there is a conflict with existing networks.

The POSTMASTER is the local part of the postmaster email address. It is recommended to setup a generic value and later configure a mail alias for that address.

The AUTH_RATELIMIT holds a security setting for fighting attackers that try to guess user passwords. The value is the limit of requests that a single IP address can perform against IMAP, POP and SMTP authentication endpoints.

The TLS_FLAVOR sets how Mailu handles TLS connections. Setting this value to notls will cause Mailu not to server any web content! More on TLS certificates.

Mail settings

The MESSAGE_SIZE_LIMIT is the maximum size of a single email. It should not be too low to avoid dropping legitimate emails and should not be too high to avoid filling the disks with large junk emails.

The RELAYNETS are network addresses for which mail is relayed for free with no authentication required. This should be used with great care. If you want other Docker services’ outbound mail to be relayed, you can set this to to include all Docker networks. The default is to leave this empty.

The RELAYHOST is an optional address of a mail server relaying all outgoing mail in following format: [HOST]:PORT. RELAYUSER and RELAYPASSWORD can be used when authentication is needed.

The FETCHMAIL_DELAY is a delay (in seconds) for the fetchmail service to go and fetch new email if available. Do not use too short delays if you do not want to be blacklisted by external services, but not too long delays if you want to receive your email in time.

The RECIPIENT_DELIMITED is a character used to delimit localpart from a custom address part. For instance, if set to +, users can use addresses like localpart+custom@domain.tld to deliver mail to localpart@domain.tld. This is useful to provide external parties with different email addresses and later classify incoming mail based on the custom part.

The DMARC_RUA and DMARC_RUF are DMARC protocol specific values. They hold the localpart for DMARC rua and ruf email addresses.

Web settings

The WEB_ADMIN contains the path to the main admin interface, while WEB_WEBMAIL contains the path to the Web email client. The WEBROOT_REDIRECT redirects all non-found queries to the set path. An empty WEBROOT_REDIRECT value disables redirecting and enables classic behavior of a 404 result when not found. All three options need a leading slash (/) to work.


WEBROOT_REDIRECT has to point to a valid path on the webserver. This means it cannot point to any services which are not enabled. For example, don’t point it to /webmail when WEBMAIL=none

Both SITENAME and WEBSITE are customization options for the panel menu in the admin interface, while SITENAME is a customization option for every Web interface.

Admin account - automatic creation

For administrative tasks, an admin user account will be needed. You can create it manually, after deploying the system, or automatically. To create it manually, follow the specific deployment method documentation.

To have the account created automatically, you just need to define a few environment variables:

INITIAL_ADMIN_ACCOUNT = ``root`` The first part of the e-mail address (
INITIAL_ADMIN_DOMAIN = ```` the domain appendix. Most probably identical to the DOMAIN variable
INITIAL_ADMIN_PW = ``password`` the chosen password for the user

Also, environment variable INITIAL_ADMIN_MODE defines how the code should behave when it will try to create the admin user:

  • create (default) Will try to create user and will raise an exception if present

  • ifmissing: if user exists, nothing happens, else it will be created

  • update: user is created or, if it exists, its password gets updated

Depending on your particular deployment you most probably will want to change the default.

Advanced settings

The PASSWORD_SCHEME is the password encryption scheme. You should use the default value, unless you are importing password from a separate system and want to keep using the old password encryption scheme.

The LOG_LEVEL setting is used by the python start-up scripts as a logging threshold. Log messages equal or higher than this priority will be printed. Can be one of: CRITICAL, ERROR, WARNING, INFO, DEBUG or NOTSET. See the python docs for more information.

Infrastructure settings

Various environment variables HOST_* can be used to run Mailu containers separately from a supported orchestrator. It is used by the various components to find the location of the other containers it depends on. They can contain an optional port number. Those variables are:

  • HOST_IMAP: the container that is running the IMAP server (default: imap, port 143)

  • HOST_LMTP: the container that is running the LMTP server (default: imap:2525)

  • HOST_HOSTIMAP: the container that is running the IMAP server for the webmail (default: imap, port 10143)

  • HOST_POP3: the container that is running the POP3 server (default: imap, port 110)

  • HOST_SMTP: the container that is running the SMTP server (default: smtp, port 25)

  • HOST_AUTHSMTP: the container that is running the authenticated SMTP server for the webnmail (default: smtp, port 10025)

  • HOST_ADMIN: the container that is running the admin interface (default: admin)

  • HOST_ANTISPAM: the container that is running the antispam service (default: antispam:11334)

  • HOST_ANTIVIRUS: the container that is running the antivirus service (default: antivirus:3310)

  • HOST_WEBMAIL: the container that is running the webmail (default: webmail)

  • HOST_WEBDAV: the container that is running the webdav server (default: webdav:5232)

  • HOST_REDIS: the container that is running the redis daemon (default: redis)

Additional variables are used to locate other containers without dialing a specific port number. It is used to either whitelist connection from these addresses or connect to containers on the docker network:

  • FRONT_ADDRESS: the nginx container address (default: front)

  • WEBMAIL_ADDRESS: the webmail container address (default: webmail)

  • IMAP_ADDRESS: the webmail container address (default: webmail)