Skip to content

Environment Variables


Values in bold are the default values. If an option doesn't work as documented here, check if you are running the latest image. The current master branch corresponds to the image



If you can't set your hostname (eg: you're in a container platform that doesn't let you) specify it via this environment variable. It will have priority over docker run --hostname, or the equivalent hostname: field in compose.yaml.

  • empty => Uses the hostname -f command to get canonical hostname for DMS to use.
  • => Specify an FQDN (fully-qualified domain name) to serve mail for. The hostname is required for DMS to function correctly.

Set the log level for DMS. This is mostly relevant for container startup scripts and change detection event feedback.

Valid values (in order of increasing verbosity) are: error, warn, info, debug and trace. The default log level is info.


Here you can adjust the log-level for Supervisor. Possible values are

  • critical => Only show critical messages
  • error => Only show erroneous output
  • warn => Show warnings
  • info => Normal informational output
  • debug => Also show debug messages

The log-level will show everything in its class and above.


Default: 5000

The User ID assigned to the static vmail user for /var/mail (Mail storage managed by Dovecot).


Default: 5000

The Group ID assigned to the static vmail group for /var/mail (Mail storage managed by Dovecot).


Configures the provisioning source of user accounts (including aliases) for user queries and authentication by services managed by DMS (Postfix and Dovecot).

OAuth2 Support

Presently DMS supports OAuth2 only as an supplementary authentication method.

  • A third-party service must provide a valid token for the user which Dovecot validates with the authentication service provider. To enable this feature reference the OAuth2 configuration example guide.
  • User accounts must be provisioned to receive mail via one of the supported ACCOUNT_PROVISIONER providers.
  • User provisioning via OIDC is planned for the future, see this tracking issue.
  • empty => use FILE
  • LDAP => use LDAP authentication
  • OIDC => use OIDC authentication (not yet implemented)
  • FILE => use local files (this is used as the default)

A second container for the ldap service is necessary (e.g. bitnami/openldap).


Set different options for mynetworks option (can be overwrite in WARNING: Adding the docker network's gateway to the list of trusted hosts, e.g. using the network or connected-networks option, can create an open relay, for instance if IPv6 is enabled on the host machine but not in Docker.

  • none => Explicitly force authentication
  • container => Container IP address only.
  • host => Add docker host (ipv4 only).
  • network => Add the docker default bridge network (; WARNING: docker-compose might use others (e.g. use PERMIT_DOCKER=connected-networks in this case.
  • connected-networks => Add all connected docker networks (ipv4 only).

Note: you probably want to set POSTFIX_INET_PROTOCOLS=ipv4 to make it work fine with Docker.


Set the timezone. If this variable is unset, the container runtime will try to detect the time using /etc/localtime, which you can alternatively mount into the container. The value of this variable must follow the pattern AREA/ZONE, i.e. of you want to use Germany's time zone, use Europe/Berlin. You can lookup all available timezones here.


Amavis content filter (used for ClamAV & SpamAssassin)

  • 0 => Amavis is disabled
  • 1 => Amavis is enabled

This page provides information on Amavis' logging statistics.

  • -1/-2/-3 => Only show errors
  • 0 => Show warnings
  • 1/2 => Show default informational output
  • 3/4/5 => log debug information (very verbose)

This enables DNS block lists in Postscreen. If you want to know which lists we are using, have a look at the default for Postfix we provide and search for postscreen_dnsbl_sites.

A Warning On DNS Block Lists

Make sure your DNS queries are properly resolved, i.e. you will most likely not want to use a public DNS resolver as these queries do not return meaningful results. We try our best to only evaluate proper return codes - this is not a guarantee that all codes are handled fine though.

Note that emails will be rejected if they don't pass the block list checks!

  • 0 => DNS block lists are disabled
  • 1 => DNS block lists are enabled

Enables MTA-STS support for outbound mail.

  • 0 => Disabled
  • 1 => Enabled

See MTA-STS for further explanation.


Enables the OpenDKIM service.

  • 1 => Enabled
  • 0 => Disabled

Enables the OpenDMARC service.

  • 1 => Enabled
  • 0 => Disabled

Enabled policyd-spf in Postfix's configuration. You will likely want to set this to 0 in case you're using Rspamd (ENABLE_RSPAMD=1).

  • 0 => Disabled
  • 1 => Enabled
  • 0 => POP3 service disabled
  • 1 => Enables POP3 service
  • 0 => Disabled
  • 1 => Enabled
  • 0 => ClamAV is disabled
  • 1 => ClamAV is enabled
  • 0 => fail2ban service disabled
  • 1 => Enables fail2ban service

If you enable Fail2Ban, don't forget to add the following lines to your compose.yaml:


Otherwise, nftables won't be able to ban IPs.

  • drop => drop packet (send NO reply)
  • reject => reject packet (send ICMP unreachable) FAIL2BAN_BLOCKTYPE=drop
  • empty => all daemons start
  • 1 => only launch postfix smtp

In the majority of cases, you want letsencrypt or manual.

self-signed can be used for testing SSL until you provide a valid certificate, note that third-parties cannot trust self-signed certificates, do not use this type in production. custom is a temporary workaround that is not officially supported.

  • empty => SSL disabled.
  • letsencrypt => Support for using certificates with Let's Encrypt provisioners. (Docs: Let's Encrypt Setup)
  • manual => Provide your own certificate via separate key and cert files. (Docs: Bring Your Own Certificates)
    • Requires: SSL_CERT_PATH and SSL_KEY_PATH ENV vars to be set to the location of the files within the container.
    • Optional: SSL_ALT_CERT_PATH and SSL_ALT_KEY_PATH allow providing a 2nd certificate as a fallback for dual (aka hybrid) certificate support. Useful for ECDSA with an RSA fallback. Presently only manual mode supports this feature.
  • custom => Provide your own certificate as a single file containing both the private key and full certificate chain. (Docs: None)
  • self-signed => Provide your own self-signed certificate files. Expects a self-signed CA cert for verification. Use only for local testing of your setup. (Docs: Self-Signed Certificates)

Please read the SSL page in the documentation for more information.

  • empty => modern
  • modern => Enables TLSv1.2 and modern ciphers only. (default)
  • intermediate => Enables TLSv1, TLSv1.1 and TLSv1.2 and broad compatibility ciphers.

Configures the handling of creating mails with forged sender addresses.

  • 0 => (not recommended) Mail address spoofing allowed. Any logged in user may create email messages with a forged sender address.
  • 1 => Mail spoofing denied. Each user may only send with his own or his alias addresses. Addresses with extension delimiters are not able to send messages.

Enables the Sender Rewriting Scheme. SRS is needed if DMS acts as forwarder. See postsrsd for further explanation.

  • 0 => Disabled
  • 1 => Enabled

In case your network interface differs from eth0, e.g. when you are using HostNetworking in Kubernetes, you can set this to whatever interface you want. This interface will then be used.

  • empty => eth0

Set how many days a virusmail will stay on the server before being deleted

  • empty => 7 days

Configure Postfix virtual_transport to deliver mail to a different LMTP client (default is a unix socket to dovecot).

Provide any valid URI. Examples:

  • empty => lmtp:unix:/var/run/dovecot/lmtp (default, configured in Postfix
  • lmtp:unix:private/dovecot-lmtp (use socket)
  • lmtps:inet:<host>:<port> (secure lmtp with starttls)
  • lmtp:<kopano-host>:2003 (use kopano as mailstore)

Set the mailbox size limit for all users. If set to zero, the size will be unlimited (default). Size is in bytes.

  • empty => 0 (no limit)
  • 1 => Dovecot quota is enabled
  • 0 => Dovecot quota is disabled

See mailbox quota.


Set the message size limit for all users. If set to zero, the size will be unlimited (not recommended!). Size is in bytes.

  • empty => 10240000 (~10 MB)

Mails larger than this limit won't be scanned. ClamAV must be enabled (ENABLE_CLAMAV=1) for this.

  • empty => 25M (25 MB)
  • empty => Managesieve service disabled
  • 1 => Enables Managesieve on port 4190

Check for updates on container start and then once a day. If an update is available, a mail is send to POSTMASTER_ADDRESS.

  • 0 => Update check disabled
  • 1 => Update check enabled

Customize the update check interval. Number + Suffix. Suffix must be 's' for seconds, 'm' for minutes, 'h' for hours or 'd' for days.

  • 1d => Check for updates once a day
  • enforce => Allow other tests to complete. Reject attempts to deliver mail with a 550 SMTP reply, and log the helo/sender/recipient information. Repeat this test the next time the client connects.
  • drop => Drop the connection immediately with a 521 SMTP reply. Repeat this test the next time the client connects.
  • ignore => Ignore the failure of this test. Allow other tests to complete. Repeat this test the next time the client connects. This option is useful for testing and collecting statistics without blocking mail.
  • maildir => uses very common Maildir format, one file contains one message
  • sdbox => (experimental) uses Dovecot high-performance mailbox format, one file contains one message
  • mdbox ==> (experimental) uses Dovecot high-performance mailbox format, multiple messages per file and multiple files per box

This option has been added in November 2019. Using other format than Maildir is considered as experimental in docker-mailserver and should only be used for testing purpose. For more details, please refer to Dovecot Documentation.


If enabled, employs reject_unknown_client_hostname to sender restrictions in Postfix's configuration.

  • 0 => Disabled
  • 1 => Enabled
  • all => Listen on all interfaces.
  • ipv4 => Listen only on IPv4 interfaces. Most likely you want this behind Docker.
  • ipv6 => Listen only on IPv6 interfaces.

Note: More details at

  • all => Listen on all interfaces
  • ipv4 => Listen only on IPv4 interfaces. Most likely you want this behind Docker.
  • ipv6 => Listen only on IPv6 interfaces.

Note: More information at

  • 0 => Spam messages will be delivered to the inbox.
  • 1 => Spam messages will be delivered to the Junk mailbox.

Routes mail identified as spam into the recipient(s) Junk mailbox (a specialized folder for junk associated to the special-use flag \Junk, handled via a Dovecot sieve script internally).


Mail is received as spam when it has been marked with either header:

  • 0 => disabled
  • 1 => Spam messages will be marked as read

Enable to treat received spam as "read" (avoids notification to MUA client of new mail).


Mail is received as spam when it has been marked with either header:


This variable defines a prefix for e-mails tagged with the X-Spam: Yes (Rspamd) or X-Spam-Flag: YES (SpamAssassin/Amavis) header.

Default: empty (no prefix will be added to e-mails)

Including trailing white-space

Add trailing white-space by quote wrapping the value: SPAM_SUBJECT='[SPAM] '



Enable or disable Rspamd.

  • 0 => disabled
  • 1 => enabled

Explicit control over running a Redis instance within the container. By default, this value will match what is set for ENABLE_RSPAMD.

The purpose of this setting is to opt-out of starting an internal Redis instance when enabling Rspamd, replacing it with your own external instance.

Configuring Rspamd for an external Redis instance

You will need to provide configuration at /etc/rspamd/local.d/redis.conf similar to:

servers = "redis.example.test:6379";
expand_keys = true;
  • 0 => Disabled
  • 1 => Enabled

This settings controls whether checks should be performed on emails coming from authenticated users (i.e. most likely outgoing emails). The default value is 0 in order to align better with SpamAssassin. We recommend reading through the Rspamd documentation on scanning outbound emails though to decide for yourself whether you need and want this feature.

Not all checks and actions are disabled

DKIM signing of e-mails will still happen.

  • 0 => No checks will be performed for authenticated users
  • 1 => All default checks will be performed for authenticated users

Controls whether the Rspamd Greylisting module is enabled. This module can further assist in avoiding spam emails by greylisting e-mails with a certain spam score.

  • 0 => Disabled
  • 1 => Enabled

When enabled,

  1. the "autolearning" feature is turned on;
  2. the Bayes classifier will be trained (with the help of Sieve scripts) when moving mails
    1. from anywhere to the Junk folder (learning this email as spam);
    2. from the Junk folder into the INBOX (learning this email as ham).


As of now, the spam learning database is global (i.e. available to all users). If one user deliberately trains it with malicious data, then it will ruin your detection rate.

This feature is suitably only for users who can tell ham from spam and users that can be trusted.

  • 0 => Disabled
  • 1 => Enabled

Can be used to enable or disable the Hfilter group module. This is used by DMS to adjust the HFILTER_HOSTNAME_UNKNOWN symbol, increasing its default weight to act similar to Postfix's reject_unknown_client_hostname, without the need to outright reject a message.

  • 0 => Disabled
  • 1 => Enabled

Can be used to control the score when the HFILTER_HOSTNAME_UNKNOWN symbol applies. A higher score is more punishing. Setting it to 15 (the default score for rejecting an e-mail) is equivalent to rejecting the email when the check fails.

Default: 6 (which corresponds to the add_header action)


Can be used to enable or disable the Neural network module. This is an experimental anti-spam weigh method using three neural networks in the configuration added here. As far as we can tell it trains itself by using other modules to find out what spam is. It will take a while (a week or more) to train its first neural network. The config trains new networks all the time and discards old networks. Since it is experimental, it is switched off by default.

  • 0 => Disabled
  • 1 => Enabled



Enables regular Postfix log summary ("pflogsumm") mail reports.

  • not set => No report
  • daily_cron => Daily report for the previous day
  • logrotate => Full report based on the mail log when it is rotated

This is a new option. The old REPORT options are still supported for backwards compatibility. If this is not set and reports are enabled with the old options, logrotate will be used.


Recipient address for Postfix log summary reports.

  • not set => Use POSTMASTER_ADDRESS
  • => Specify the recipient address(es)

Sender address (FROM) for pflogsumm reports (if Postfix log summary reports are enabled).

  • not set => Use REPORT_SENDER
  • => Specify the sender address

Interval for logwatch report.

  • none => No report is generated
  • daily => Send a daily report
  • weekly => Send a report every week

Recipient address for logwatch reports if they are enabled.

  • => Specify the recipient address(es)

Sender address (FROM) for logwatch reports if logwatch reports are enabled.

  • not set => Use REPORT_SENDER
  • => Specify the sender address

Defines who receives reports (if they are enabled).

  • => Specify the recipient address

Defines who sends reports (if they are enabled).

  • empty => mailserver-report@<YOUR DOMAIN>
  • => Specify the sender address

Changes the interval in which log files are rotated.

  • weekly => Rotate log files weekly
  • daily => Rotate log files daily
  • monthly => Rotate log files monthly


LOGROTATE_INTERVAL only manages logrotate within the container for services we manage internally.

The entire log output for the container is still available via docker logs mailserver (or your respective container name). If you want to configure external log rotation for that container output as well, : Docker Logging Drivers.

By default, the logs are lost when the container is destroyed (eg: re-creating via docker compose down && docker compose up -d). To keep the logs, mount a volume (to /var/log/mail/).


This variable can also determine the interval for Postfix's log summary reports, see PFLOGSUMM_TRIGGER.


Defines how many files are kept by logrotate.

  • 4 => Number of files


  • 0 => SpamAssassin is disabled
  • 1 => SpamAssassin is enabled
SpamAssassin analyzes incoming mail and assigns a spam score

Integration with Amavis involves processing mail based on the assigned spam score via SA_TAG, SA_TAG2 and SA_KILL.

These settings have equivalent ENV supported by DMS for easy adjustments, as documented below.

  • 0 => KAM disabled
  • 1 => KAM enabled

KAM is a 3rd party SpamAssassin ruleset, provided by the McGrail Foundation. If SpamAssassin is enabled, KAM can be used in addition to the default ruleset.

  • 0 => (Amavis action: D_BOUNCE): Spam messages will be bounced (rejected) without any notification (dangerous).
  • 1 => (Amavis action: D_PASS): Spam messages will be delivered to the inbox.


The Amavis action configured by this setting:

  • Influences the behavior of the SA_KILL setting.
  • Applies to the Amavis config parameters $final_spam_destiny and $final_bad_header_destiny.

This ENV setting is related to

  • 2.0 => add 'spam info' headers at, or above this spam score

Mail is not yet considered spam at this spam score, but for purposes like diagnostics it can be useful to identify mail with a spam score at a lower bound than SA_TAG2.

X-Spam headers appended to mail

Send a simple mail to a local DMS account

docker exec dms swaks --server --to --body 'spam'

Inspecting the raw mail you will notice several X-Spam headers were added to the mail like this:

X-Spam-Flag: NO
X-Spam-Score: 4.162
X-Spam-Level: ****
X-Spam-Status: No, score=4.162 tagged_above=2 required=4
        NO_DNS_FOR_FROM=0.379, NO_RECEIVED=-0.001, NO_RELAYS=-0.001,
        PYZOR_CHECK=1.985] autolearn=no autolearn_force=no

The X-Spam-Score is 4.162

High enough for SA_TAG to trigger adding these headers, but not high enough for SA_TAG2 (which would set X-Spam-Flag: YES instead).

  • 6.31 => add 'spam detected' headers at, or above this level

When a spam score is high enough, mark mail as spam (Appends the mail header: X-Spam-Flag: YES).

Interaction with other ENV

  • SPAM_SUBJECT modifies the mail subject to better communicate spam mail to the user.
  • MOVE_SPAM_TO_JUNK=1: The mail is still delivered, but to the recipient(s) junk folder instead. This feature reduces the usefulness of SPAM_SUBJECT.
  • 10.0 => quarantine + triggers action to handle spam

Controls the spam score threshold for triggering an action on mail that has a high spam score.

Choosing an appropriate SA_KILL value

The value should be high enough to be represent confidence in mail as spam:

  • Too low: The action taken may prevent legitimate mail (ham) that was incorrectly detected as spam from being delivered successfully.
  • Too high: Allows more spam to bypass the SA_KILL trigger (how to treat mail with high confidence that it is actually spam).

Experiences from DMS users with these settings has been collected here, along with some direct configuration guides (under "Resources for references").

Trigger action

DMS will configure Amavis with either of these actions based on the DMS SPAMASSASSIN_SPAM_TO_INBOX ENV setting:

  • D_PASS (default):
    • Accept mail and deliver it to the recipient(s), despite the high spam score. A copy is still stored in quarantine.
    • This is a good default to start with until you are more confident in an SA_KILL threshold that won't accidentally discard / bounce legitimate mail users are expecting to arrive but is detected as spam.
    • Additionally sends a bounce notification (DSN).
    • The DSN is suppressed (no bounce sent) when the spam score exceeds the Amavis $sa_dsn_cutoff_level config setting (default: 10). With the DMS SA_KILL default also being 10, no DSN will ever be sent.
    • These two aren't configured by DMS, but are valid alternative action values if configuring Amavis directly.
Quarantined mail

When mail has a spam score that reaches the SA_KILL threshold:

  • It will be quarantined regardless of the SA_KILL action to perform.
  • With D_PASS the delivered mail also appends an X-Quarantine-ID mail header. The ID value of this header is part of the quarantined file name.

If emails are quarantined, they are compressed and stored at a location:

  • Default: /var/lib/amavis/virusmails/
  • When the /var/mail-state/ volume is present: /var/mail-state/lib-amavis/virusmails/


Easily list mail stored in quarantine with find and the quarantine path:

find /var/lib/amavis/virusmails -type f
  • 1 => will activate SpamAssassin short circuiting for bayes spam detection.

This will uncomment the respective line in /etc/spamassasin/


Activate this only if you are confident in your bayes database for identifying spam.

  • 1 => will activate SpamAssassin short circuiting for bayes ham detection

This will uncomment the respective line in /etc/spamassasin/


Activate this only if you are confident in your bayes database for identifying ham.


  • 0 => fetchmail disabled
  • 1 => fetchmail enabled
  • 300 => fetchmail The number of seconds for the interval
  • 0 => fetchmail runs with a single config file /etc/fetchmailrc
  • 1 => /etc/fetchmailrc is split per poll entry. For every poll entry a separate fetchmail instance is started to allow having multiple imap idle connections per server (when poll entries reference the same IMAP server).

Note: The defaults of your fetchmailrc file need to be at the top of the file. Otherwise it won't be added correctly to all separate fetchmail instances.



Enable or disable getmail.

  • 0 => Disabled
  • 1 => Enabled
  • 5 => getmail The number of minutes for the interval. Min: 1; Max: 30; Default: 5.


  • empty => OAUTH2 authentication is disabled
  • 1 => OAUTH2 authentication is enabled
  • => Specify the user info endpoint URL of the oauth2 provider (eg:


  • empty => no
  • yes => LDAP over TLS enabled for Postfix
  • empty =>
  • => Specify the <dns-name> / <ip-address> where the LDAP server is reachable via a URI like: ldaps://
  • Note: You must include the desired URI scheme (ldap://, ldaps://, ldapi://).
  • empty => ou=people,dc=domain,dc=com
  • => e.g. LDAP_SEARCH_BASE=dc=mydomain,dc=local
  • empty => cn=admin,dc=domain,dc=com
  • => take a look at examples of SASL_LDAP_BIND_DN
  • empty => admin
  • => Specify the password to bind against ldap
  • e.g. (&(mail=%s)(mailEnabled=TRUE))
  • => Specify how ldap should be asked for users
  • e.g. (&(mailGroupMember=%s)(mailEnabled=TRUE))
  • => Specify how ldap should be asked for groups
  • e.g. (&(mailAlias=%s)(mailEnabled=TRUE))
  • => Specify how ldap should be asked for aliases
  • e.g. (&(|(mail=*@%s)(mailalias=*@%s)(mailGroupMember=*@%s))(mailEnabled=TRUE))
  • => Specify how ldap should be asked for domains
  • empty => use user/alias/group maps directly, equivalent to (|($LDAP_QUERY_FILTER_USER)($LDAP_QUERY_FILTER_ALIAS)($LDAP_QUERY_FILTER_GROUP))
  • => Override how ldap should be asked if a sender address is allowed for a user
  • empty => no
  • yes => LDAP over TLS enabled for Dovecot


The following variables overwrite the default values for /etc/dovecot/dovecot-ldap.conf.ext.

  • empty => same as LDAP_SEARCH_BASE
  • => Tell Dovecot to search only below this base entry. (e.g. ou=people,dc=domain,dc=com)
  • empty => SSHA
  • => Select one crypt scheme for password hashing from this list of password schemes.
  • empty => same as LDAP_BIND_DN
  • => Bind dn for LDAP connection. (e.g. cn=admin,dc=domain,dc=com)
  • empty => same as LDAP_BIND_PW
  • => Password for LDAP dn specified in DOVECOT_DN.
  • empty => same as LDAP_SERVER_HOST
  • => Specify a space separated list of LDAP URIs.
  • Note: You must include the desired URI scheme (ldap://, ldaps://, ldapi://).
  • empty => 3
  • 2 => LDAP version 2 is used
  • 3 => LDAP version 3 is used
  • e.g. (&(objectClass=PostfixBookMailAccount)(uniqueIdentifier=%n))
  • e.g. homeDirectory=home,qmailUID=uid,qmailGID=gid,mailMessageStore=mail
  • => Specify the directory to dovecot attribute mapping that fits your directory structure.
  • Note: This is necessary for directories that do not use the Postfix Book Schema.
  • Note: The left-hand value is the directory attribute, the right hand value is the dovecot variable.
  • More details on the Dovecot Wiki
  • e.g. (&(objectClass=PostfixBookMailAccount)(uniqueIdentifier=%n))
  • empty => same as DOVECOT_USER_FILTER
  • e.g. uid=user,userPassword=password
  • => Specify the directory to dovecot variable mapping that fits your directory structure.
  • Note: This is necessary for directories that do not use the Postfix Book Schema.
  • Note: The left-hand value is the directory attribute, the right hand value is the dovecot variable.
  • More details on the Dovecot Wiki


  • 0 => postgrey is disabled
  • 1 => postgrey is enabled
  • 300 => greylist for N seconds

Note: This postgrey setting needs ENABLE_POSTGREY=1

  • 35 => delete entries older than N days since the last time that they have been seen

Note: This postgrey setting needs ENABLE_POSTGREY=1

  • 5 => whitelist host after N successful deliveries (N=0 to disable whitelisting)

Note: This postgrey setting needs ENABLE_POSTGREY=1

  • Delayed by Postgrey => response when a mail is greylisted

Note: This postgrey setting needs ENABLE_POSTGREY=1


  • 0 => saslauthd is disabled
  • 1 => saslauthd is enabled
  • empty => pam
  • ldap => authenticate against ldap server
  • shadow => authenticate against local user db
  • mysql => authenticate against mysql db
  • rimap => authenticate against imap server
  • NOTE: can be a list of mechanisms like pam ldap shadow
  • empty => None
  • e.g. with SASLAUTHD_MECHANISMS rimap you need to specify the ip-address/servername of the imap server ==>
  • empty => same as LDAP_SERVER_HOST
  • Note: You must include the desired URI scheme (ldap://, ldaps://, ldapi://).
  • empty => no
  • yes => Enable ldap_start_tls option
  • empty => no
  • yes => Enable ldap_tls_check_peer option

Path to directory with CA (Certificate Authority) certificates.

  • empty => Nothing is added to the configuration
  • Any value => Fills the ldap_tls_cacert_dir option

File containing CA (Certificate Authority) certificate(s).

  • empty => Nothing is added to the configuration
  • Any value => Fills the ldap_tls_cacert_file option
  • empty => same as LDAP_BIND_DN
  • specify an object with privileges to search the directory tree
  • e.g. active directory: SASLAUTHD_LDAP_BIND_DN=cn=Administrator,cn=Users,dc=mydomain,dc=net
  • e.g. openldap: SASLAUTHD_LDAP_BIND_DN=cn=admin,dc=mydomain,dc=net
  • empty => same as LDAP_BIND_PW
  • empty => same as LDAP_SEARCH_BASE
  • specify the search base
  • empty => default filter (&(uniqueIdentifier=%u)(mailEnabled=TRUE))
  • e.g. for active directory: (&(sAMAccountName=%U)(objectClass=person))
  • e.g. for openldap: (&(uid=%U)(objectClass=person))

Specify what password attribute to use for password verification.

  • empty => Nothing is added to the configuration but the documentation says it is userPassword by default.
  • Any value => Fills the ldap_password_attr option
  • empty => bind will be used as a default value
  • fastbind => The fastbind method is used
  • custom => The custom method uses userPassword attribute to verify the password

Specify the authentication mechanism for SASL bind.

  • empty => Nothing is added to the configuration
  • Any value => Fills the ldap_mech option

SRS (Sender Rewriting Scheme)


An email has an "envelope" sender (indicating the sending server) and a "header" sender (indicating who sent it). More strict SPF policies may require you to replace both instead of just the envelope sender.

More info.

  • envelope_sender => Rewrite only envelope sender address
  • header_sender => Rewrite only header sender (not recommended)
  • envelope_sender,header_sender => Rewrite both senders
  • empty => Envelope sender will be rewritten for all domains
  • provide comma separated list of domains to exclude from rewriting
  • empty => generated when the container is started for the first time
  • provide a secret to use in base64
  • you may specify multiple keys, comma separated. the first one is used for signing and the remaining will be used for verification. this is how you rotate and expire keys
  • if you have a cluster/swarm make sure the same keys are on all nodes
  • example command to generate a key: dd if=/dev/urandom bs=24 count=1 2>/dev/null | base64
  • empty => Derived from OVERRIDE_HOSTNAME, $DOMAINNAME (internal), or the container's hostname
  • Set this if auto-detection fails, isn't what you want, or you wish to have a separate container handle DSNs

Relay Host

Supported ENV for the Relay Host feature.


This is advised unless you need support for sender domain opt-out (via setup relay exclude-domain).

The implementation for RELAY_HOST is not compatible with LDAP.

Opt-in for relay host support

Enable relaying only for specific sender domains instead by using setup relay add-domain.

NOTE: Presently there is a caveat when relay host credentials are configured (which is incompatible with opt-in).


Configures a default relay host.


  • All mail sent outbound from DMS will be relayed through the configured host, unless sender-dependent relayhost maps have been configured (which have precedence).
  • The host value may optionally be wrapped in brackets (skips DNS query for MX record): []:587 vs

Technical Details

This ENV internally configures the Postfix setting: relayhost


Configures a default relay host.


Expects a value like Internally this will be wrapped to [], so it should resolve to the MTA directly.

Do not use with DEFAULT_RELAY_HOST

RELAY_HOST has precedence as it is configured with sender_dependent_relayhost_maps.


  • This is a legacy ENV. It is however required for the opt-out feature of to work.
  • Internal configuration however differs from DEFAULT_RELAY_HOST.

Technical Details

This feature is configured internally using the:

All known mail domains managed by DMS will be configured to relay outbound mail to RELAY_HOST by adding them implicitly to /etc/postfix/relayhost_map, except for domains using the opt-out feature of


Default => 25

Support for configuring a different port than 25 for RELAY_HOST to use.


Requires RELAY_HOST.

Relay Host Credentials

Configuring relay host credentials enforces outbound authentication

Presently when RELAY_USER + RELAY_PASSWORD or are configured, all outbound mail traffic is configured to require a secure connection established and forbids the omission of credentials.

Additional feature work is required to only enforce these requirements on mail sent through a configured relay host.


Provide the credentials to use with RELAY_HOST or DEFAULT_RELAY_HOST.

Alternative credentials config

You may prefer to use setup relay add-auth to avoid risking ENV exposing secrets.

  • With the CLI command, you must provide relay credentials for each of your sender domains.
  • Alternatively manually edit with the correct relayhost entry (DEFAULT_RELAY_HOST value, or as defined in /etc/postfix/relayhost_map) to provide credentials per relayhost configured.

Technical Details

Credentials for relay hosts are configured internally using the:

When is present, DMS will copy it internally to /etc/postfix/sasl_passwd.

  • DMS provides support for mapping credentials by sender domain:
    • Explicitly via setup relay add-auth (creates / updates
    • Implicitly via the relay ENV support (configures all known DMS managed domains to use the relay ENV).
  • Credentials can be explicitly configured for specific relay hosts instead of sender domains:
    • Add the exact relayhost value (host:port / [host]:port) from the generated /etc/postfix/relayhost_map, or (DEFAULT_RELAY_HOST).
    • setup relay ... is missing support, you must instead add these manually to