You are currently browsing documentation for the master branch. Documentation for the stable 1.8 branch can be found here.

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 WILDCARD_SENDERS setting is a comma delimited list of user email addresses that are allowed to send emails from any existing address (spoofing the sender).

The AUTH_RATELIMIT_IP (default: 60/hour) holds a security setting for fighting attackers that waste server resources by trying to guess user passwords (typically using a password spraying attack). The value defines the limit of authentication attempts that will be processed on non-existing accounts for a specific IP subnet (as defined in AUTH_RATELIMIT_IP_V4_MASK and AUTH_RATELIMIT_IP_V6_MASK below).

The AUTH_RATELIMIT_USER (default: 100/day) holds a security setting for fighting attackers that attempt to guess a user’s password (typically using a password bruteforce attack). The value defines the limit of authentication attempts allowed for any given account within a specific timeframe.

The AUTH_RATELIMIT_EXEMPTION_LENGTH (default: 86400) is the number of seconds after a successful login for which a specific IP address is exempted from rate limits. This ensures that users behind a NAT don’t get locked out when a single client is misconfigured… but also potentially allow for users to attack each-other.

The AUTH_RATELIMIT_EXEMPTION (default: ‘’) is a comma separated list of network CIDRs that won’t be subject to any form of rate limiting. Specifying, ::/0 there is a good way to disable rate limiting altogether.

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 MESSAGE_RATELIMIT is the limit of messages a single user can send. This is meant to fight outbound spam in case of compromised or malicious account on the server.

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.

By default postfix uses “opportunistic TLS” for outbound mail. This can be changed by setting OUTBOUND_TLS_LEVEL to encrypt or secure. This setting is highly recommended if you are using a relayhost that supports TLS but discouraged otherwise. DEFER_ON_TLS_ERROR (default: True) controls whether incomplete policies (DANE without DNSSEC or “testing” MTA-STS policies) will be taken into account and whether emails will be defered if the additional checks enforced by those policies fail.

Similarily by default nginx uses “opportunistic TLS” for inbound mail. This can be changed by setting INBOUND_TLS_ENFORCE to True. Please note that this is forbidden for internet facing hosts according to e.g. RFC 3207 , because this prevents MTAs without STARTTLS support or e.g. mismatching TLS versions to deliver emails to Mailu.

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_DELIMITER is a list of characters used to delimit localpart from a custom address part. For instance, if set to +-, users can use addresses like or to deliver mail to 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.

Full-text search is enabled for IMAP is enabled by default. This feature can be disabled (e.g. for performance reasons) by setting the optional variable FULL_TEXT_SEARCH to off.

Web settings

  • WEB_ADMIN contains the path to the main admin interface

  • WEB_WEBMAIL contains the path to the Web email client.

  • 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. Alternatively, WEBROOT_REDIRECT can be set to none if you are using an Nginx override for location /.

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.

  • LOGO_BACKGROUND sets a custom background colour for the brand logo in the topleft of the main admin interface. For a list of colour codes refer to this page of w3schools.

  • LOGO_URL sets a URL for a custom logo. This logo replaces the Mailu logo in the topleft of the main admin 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 CREDENTIAL_ROUNDS (default: 12) setting is the number of rounds used by the password hashing scheme. The number of rounds can be reduced in case faster authentication is needed or increased when additional protection is desired. Keep in mind that this is a mitigation against offline attacks on password hashes, aiming to prevent credential stuffing (due to password re-use) on other systems.

The SESSION_COOKIE_SECURE (default: True) setting controls the secure flag on the cookies of the administrative interface. It should only be turned off if you intend to access it over plain HTTP.

SESSION_LIFETIME (default: 24) is the length in hours a session is valid for on the administrative interface.

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.

The LETSENCRYPT_SHORTCHAIN (default: False) setting controls whether we send the ISRG Root X1 certificate in TLS handshakes. This is required for android handsets older than 7.1.1 but slows down the performance of modern devices.

The REAL_IP_HEADER (default: unset) and REAL_IP_FROM (default: unset) settings controls whether HTTP headers such as X-Forwarded-For or X-Real-IP should be trusted. The former should be the name of the HTTP header to extract the client IP address from and the later a comma separated list of IP addresses designing which proxies to trust. If you are using Mailu behind a reverse proxy, you should set both. Setting the former without the later introduces a security vulnerability allowing a potential attacker to spoof his source address.

Antivirus settings

The ANTIVIRUS_ACTION switches behaviour if a virus is detected. It defaults to ‘discard’, so any detected virus is silently discarded. If set to ‘reject’, rspamd is configured to reject virus mails during SMTP dialogue, so the sender will receive a reject message.

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_MILTER: the container that is running the antispam milter service (default: antispam:11332)

  • HOST_ANTISPAM_WEBUI: the container that is running the antispam webui 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)

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

The startup scripts will resolve HOST_* to their IP addresses and store the result in *_ADDRESS for further use.

Alternatively, *_ADDRESS can directly be set. In this case, the values of *_ADDRESS is kept and not resolved. This can be used to rely on DNS based service discovery with changing services IP addresses. When using *_ADDRESS, the hostnames must be full-qualified hostnames. Otherwise nginx will not be able to resolve the hostnames.

Database settings

The admin service stores configurations in a database.

  • DB_FLAVOR: the database type for mailu admin service. (sqlite, postgresql, mysql)

  • DB_HOST: the database host for mailu admin service. (when not sqlite)

  • DB_PORT: the database port for mailu admin service. (when not sqlite)

  • DB_PW: the database password for mailu admin service. (when not sqlite)

  • DB_USER: the database user for mailu admin service. (when not sqlite)

  • DB_NAME: the database name for mailu admin service. (when not sqlite)

The roundcube service stores configurations in a database.

  • ROUNDCUBE_DB_FLAVOR: the database type for roundcube service. (sqlite, postgresql, mysql)

  • ROUNDCUBE_DB_HOST: the database host for roundcube service. (when not sqlite)

  • ROUNDCUBE_DB_PORT: the database port for roundcube service. (when not sqlite)

  • ROUNDCUBE_DB_PW: the database password for roundcube service. (when not sqlite)

  • ROUNDCUBE_DB_USER: the database user for roundcube service. (when not sqlite)

  • ROUNDCUBE_DB_NAME: the database name for roundcube service. (when not sqlite)