This page explains the variables found in
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.
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
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
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.
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.
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
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).
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_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.
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.
AUTH_RATELIMIT_EXEMPTION (default: ‘’) is a comma separated list of network
CIDRs that won’t be subject to any form of rate limiting. Specifying
there is a good way to disable rate limiting altogether.
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.
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.
MESSAGE_RATELIMIT (default: 200/day) is the maximum number of messages
a single user can send.
MESSAGE_RATELIMIT_EXEMPTION contains a comma delimited
list of user email addresses that are exempted from any restriction. Those
settings are meant to reduce outbound spam in case of compromised or malicious
account on the server.
RELAYNETS (default: unset) is a comma delimited list of network addresses
for which mail is relayed for with no authentication required. This should be
used with great care as misconfigurations may turn your Mailu instance into an
RELAYHOST is an optional address to use as a smarthost for all outgoing
mail in following format:
can be used when authentication is required.
By default postfix uses “opportunistic TLS” for outbound mail. This can be changed
secure. This setting is
highly recommended if you are using a relayhost that supports TLS but discouraged
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
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.
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.
RECIPIENT_DELIMITER is a list of characters used to delimit localpart
from a custom address part. For instance, if set to
+-, users can use
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.
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
WEB_ADMINcontains the path to the main admin interface
WEB_WEBMAILcontains the path to the Web email client.
WEBROOT_REDIRECTredirects all non-found queries to the set path. An empty
WEBROOT_REDIRECTvalue disables redirecting and enables classic behavior of a 404 result when not found. Alternatively,
WEBROOT_REDIRECTcan be set to
noneif you are using an Nginx override for
All three options need a leading slash (
/) to work.
WEBROOT_REDIRECThas 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
WEBSITE are customization options for the panel menu
in the admin interface, while
SITENAME is a customization option for
every Web interface.
LOGO_BACKGROUNDsets 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_URLsets 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: the admin username: The first part of the e-mail address before the @.
INITIAL_ADMIN_DOMAIN: the domain appendix: Most probably identical to the
INITIAL_ADMIN_PW: the admin password.
INITIAL_ADMIN_MODE: use one of the options below for configuring how the admin account must be created:
create: (default) creates a new admin account and raises an exception when it already exists.
ifmissing: creates a new admin account when the admin account does not exist.
update: creates a new admin account when it does not exist, or update the password of an existing admin account.
Note: It is recommended to set
INITIAL_ADMIN_MODE to either
ifmissing. Leaving it with the default value will cause an error when the system is restarted.
Depending on your particular deployment you most probably will want to change the default.
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.
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_TIMEOUT (default: 3600) is the maximum amount of time in seconds between requests before a session is invalidated.
PERMANENT_SESSION_LIFETIME (default: 108000) is the maximum amount of time in seconds a session can be kept alive for if it hasn’t timed-out.
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.
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.
REAL_IP_HEADER (default: unset) and
REAL_IP_FROM (default: unset) settings controls whether HTTP headers such as
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 designating 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.
TZ sets the timezone Mailu will use. The timezone naming convention usually uses a
Region/City format. See TZ database name for a list of valid timezones This defaults to
Etc/UTC. Warning: if you are observing different timestamps in your log files you should change your hosts timezone to UTC instead of changing TZ to your local timezone. Using UTC allows easy log correlation with remote MTAs.
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.
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:
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:
HOST_ANTISPAM_MILTER: the container that is running the antispam milter service (default:
HOST_ANTISPAM_WEBUI: the container that is running the antispam webui service (default:
HOST_ANTIVIRUS: the container that is running the antivirus service (default:
HOST_WEBMAIL: the container that is running the webmail (default:
HOST_WEBDAV: the container that is running the webdav server (default:
HOST_REDIS: the container that is running the redis daemon (default:
HOST_WEBMAIL: the container that is running the webmail (default:
The startup scripts will resolve
HOST_* to their IP addresses and store the result in
*_ADDRESS for further use.
*_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.
*_ADDRESS, the hostnames must be full-qualified hostnames. Otherwise nginx will not be able to
resolve the hostnames.
The admin service stores configurations in a database.
DB_FLAVOR: the database type for mailu admin service. (
DB_HOST: the database host for mailu admin service. For non-default ports use the notation host:port. (when not
DB_PW: the database password for mailu admin service. (when not
DB_USER: the database user for mailu admin service. (when not
DB_NAME: the database name for mailu admin service. (when not
The roundcube service stores configurations in a database.
ROUNDCUBE_DB_FLAVOR: the database type for roundcube service. (
ROUNDCUBE_DB_HOST: the database host for roundcube service. For non-default ports use the notation host:port. (when not
ROUNDCUBE_DB_PW: the database password for roundcube service. (when not
ROUNDCUBE_DB_USER: the database user for roundcube service. (when not
ROUNDCUBE_DB_NAME: the database name for roundcube service. (when not
When using roundcube it is possible to select the plugins to be enabled by setting
a comma separated list of plugin-names. Included plugins are:
acl (needs configuration)
additional_message_headers (needs configuration)
show_additional_headers (needs configuration)
ROUNDCUBE_PLUGINS is not set the following plugins are enabled by default:
To disable all plugins just set
To configure a plugin add php files named
*.inc to roundcube’s override section.
Mail log settings
By default, all services log directly to stdout/stderr. Logs can be collected by any docker log processing solution.
Postfix writes the logs to a syslog server which logs to stdout. This is used to filter out messages from the healthcheck. In some situations, a separate mail log is required (e.g. for legal reasons). The syslog server can be configured to write log files to a volume. It can be configured with the following option:
POSTFIX_LOG_FILE: The file to log the mail log to. When enabled, the syslog server will also log to stdout.
POSTFIX_LOG_FILE is enabled, the logrotate program will automatically rotate the logs every week and keep 52 logs.
To override the logrotate configuration, create the file logrotate.conf with the desired configuration in the Postfix overrides folder.