docker-mailserver/docs/content/config/environment.md

title
Environment Variables

!!! info

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 `mailserver/docker-mailserver:edge`.

General

OVERRIDE_HOSTNAME

• empty => uses the hostname command to get canonical hostname for docker-mailserver to use.
• => Specify a fully-qualified domainname to serve mail for. This is used for many of the config features so 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 take priority over docker run options: --hostname and --domainname, or docker-compose.yml config equivalents: hostname: and domainname:.

DMS_DEBUG

This environment variable is deprecated. Use LOG_LEVEL instead.

• 0 => Debug disabled
• 1 => Enables debug on startup

LOG_LEVEL

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.

SUPERVISOR_LOGLEVEL

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.

ONE_DIR

• 0 => state in default directories.
• 1 => consolidate all states into a single directory (/var/mail-state) to allow persistence using docker volumes. See the related FAQ entry for more information.

PERMIT_DOCKER

Set different options for mynetworks option (can be overwrite in postfix-main.cf) 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 (172.16.0.0/12); WARNING: docker-compose might use others (e.g. 192.168.0.0/16) 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.

ENABLE_AMAVIS

Amavis content filter (used for ClamAV & SpamAssassin)

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

AMAVIS_LOGLEVEL

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)

ENABLE_DNSBL

This enables the zen.spamhaus.org DNS block list in postfix and various lists in postscreen.

Note: 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

ENABLE_CLAMAV

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

ENABLE_POP3

• empty => POP3 service disabled
• 1 => Enables POP3 service

ENABLE_FAIL2BAN

• 0 => fail2ban service disabled
• 1 => Enables fail2ban service

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

cap_add:
  - NET_ADMIN

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

FAIL2BAN_BLOCKTYPE

• drop => drop packet (send NO reply)
• reject => reject packet (send ICMP unreachable) FAIL2BAN_BLOCKTYPE=drop

SMTP_ONLY

• empty => all daemons start
• 1 => only launch postfix smtp

SSL_TYPE

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.

TLS_LEVEL

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

SPOOF_PROTECTION

Configures the handling of creating mails with forged sender addresses.

• empty => Mail address spoofing allowed. Any logged in user may create email messages with a forged sender address. See also Wikipedia(not recommended, but default for backwards compatibility reasons)
• 1 => (recommended) 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.

ENABLE_SRS

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

• 0 => Disabled
• 1 => Enabled

NETWORK_INTERFACE

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

VIRUSMAILS_DELETE_DELAY

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

• empty => 7 days

ENABLE_POSTFIX_VIRTUAL_TRANSPORT

This Option is activating the Usage of POSTFIX_DAGENT to specify a ltmp client different from default dovecot socket.

• empty => disabled
• 1 => enabled

POSTFIX_DAGENT

Enabled by ENABLE_POSTFIX_VIRTUAL_TRANSPORT. Specify the final delivery of postfix

• empty: fail
• lmtp:unix:private/dovecot-lmtp (use socket)
• lmtps:inet:<host>:<port> (secure lmtp with starttls, take a look at https://sys4.de/en/blog/2014/11/17/sicheres-lmtp-mit-starttls-in-dovecot/)
• lmtp:<kopano-host>:2003 (use kopano as mailstore)
• etc.

POSTFIX_MAILBOX_SIZE_LIMIT

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

• empty => 0 (no limit)

ENABLE_QUOTAS

• 1 => Dovecot quota is enabled
• 0 => Dovecot quota is disabled

See mailbox quota.

POSTFIX_MESSAGE_SIZE_LIMIT

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

• empty => 10240000 (~10 MB)

CLAMAV_MESSAGE_SIZE_LIMIT

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

• empty => 25M (25 MB)

ENABLE_MANAGESIEVE

• empty => Managesieve service disabled
• 1 => Enables Managesieve on port 4190

POSTMASTER_ADDRESS

• empty => postmaster@example.com
• => Specify the postmaster address

ENABLE_UPDATE_CHECK

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

UPDATE_CHECK_INTERVAL

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

POSTSCREEN_ACTION

• 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.

DOVECOT_MAILBOX_FORMAT

• 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.

POSTFIX_INET_PROTOCOLS

• 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 http://www.postfix.org/postconf.5.html#inet_protocols

DOVECOT_INET_PROTOCOLS

• 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 https://dovecot.org/doc/dovecot-example.conf

Reports

PFLOGSUMM_TRIGGER

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.

PFLOGSUMM_RECIPIENT

Recipient address for Postfix log summary reports.

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

PFLOGSUMM_SENDER

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

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

LOGWATCH_INTERVAL

Interval for logwatch report.

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

LOGWATCH_RECIPIENT

Recipient address for logwatch reports if they are enabled.

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

LOGWATCH_SENDER

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

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

REPORT_RECIPIENT

Defines who receives reports (if they are enabled).

• empty => Use POSTMASTER_ADDRESS
• => Specify the recipient address

REPORT_SENDER

Defines who sends reports (if they are enabled).

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

LOGROTATE_INTERVAL

Changes the interval in which log files are rotated.

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

!!! note

`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](https://docs.docker.com/config/containers/logging/configure/).

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/`).

!!! note

This variable can also determine the interval for Postfix's log summary reports, see [`PFLOGSUMM_TRIGGER`](#pflogsumm_trigger).

SpamAssassin

ENABLE_SPAMASSASSIN

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

SPAMASSASSIN_SPAM_TO_INBOX

• 0 => Spam messages will be bounced (rejected) without any notification (dangerous).
• 1 => Spam messages will be delivered to the inbox and tagged as spam using SA_SPAM_SUBJECT.

ENABLE_SPAMASSASSIN_KAM

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 => KAM disabled
• 1 => KAM enabled

MOVE_SPAM_TO_JUNK

Spam messages can be moved in the Junk folder. Note: this setting needs SPAMASSASSIN_SPAM_TO_INBOX=1

• 0 => Spam messages will be delivered in the mailbox.
• 1 => Spam messages will be delivered in the Junk folder.

SA_TAG

• 2.0 => add spam info headers if at, or above that level

Note: this SpamAssassin setting needs ENABLE_SPAMASSASSIN=1

SA_TAG2

• 6.31 => add 'spam detected' headers at that level

Note: this SpamAssassin setting needs ENABLE_SPAMASSASSIN=1

SA_KILL

• 6.31 => triggers spam evasive actions

!!! note "This SpamAssassin setting needs ENABLE_SPAMASSASSIN=1"

By default, `docker-mailserver` is configured to quarantine spam emails.

If emails are quarantined, they are compressed and stored in a location dependent on the `ONE_DIR` setting above. To inhibit this behaviour and deliver spam emails, set this to a very high value e.g. `100.0`.

If `ONE_DIR=1` (default) the location is `/var/mail-state/lib-amavis/virusmails/`, or if `ONE_DIR=0`: `/var/lib/amavis/virusmails/`. These paths are inside the docker container.

SA_SPAM_SUBJECT

• ***SPAM*** => add tag to subject if spam detected

Note: this SpamAssassin setting needs ENABLE_SPAMASSASSIN=1. Add the SpamAssassin score to the subject line by inserting the keyword _SCORE_: ***SPAM(_SCORE_)***.

SA_SHORTCIRCUIT_BAYES_SPAM

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

This will uncomment the respective line in /etc/spamassasin/local.cf

Note: activate this only if you are confident in your bayes database for identifying spam.

SA_SHORTCIRCUIT_BAYES_HAM

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

This will uncomment the respective line in /etc/spamassasin/local.cf

Note: activate this only if you are confident in your bayes database for identifying ham.

Fetchmail

ENABLE_FETCHMAIL

• 0 => fetchmail disabled
• 1 => fetchmail enabled

FETCHMAIL_POLL

• 300 => fetchmail The number of seconds for the interval

FETCHMAIL_PARALLEL

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 configurations defined.

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.

LDAP

ENABLE_LDAP

• empty => LDAP authentification is disabled
• 1 => LDAP authentification is enabled
• NOTE:
  • A second container for the ldap service is necessary (e.g. docker-openldap)
  • For preparing the ldap server to use in combination with this container this article may be helpful

LDAP_START_TLS

• empty => no
• yes => LDAP over TLS enabled for Postfix

LDAP_SERVER_HOST

• empty => mail.example.com
• => Specify the dns-name/ip-address where the ldap-server is listening, or an URI like ldaps://mail.example.com
• NOTE: If you going to use docker-mailserver in combination with docker-compose.yml you can set the service name here

LDAP_SEARCH_BASE

• empty => ou=people,dc=domain,dc=com
• => e.g. LDAP_SEARCH_BASE=dc=mydomain,dc=local

LDAP_BIND_DN

• empty => cn=admin,dc=domain,dc=com
• => take a look at examples of SASL_LDAP_BIND_DN

LDAP_BIND_PW

• empty => admin
• => Specify the password to bind against ldap

LDAP_QUERY_FILTER_USER

• e.g. (&(mail=%s)(mailEnabled=TRUE))
• => Specify how ldap should be asked for users

LDAP_QUERY_FILTER_GROUP

• e.g. (&(mailGroupMember=%s)(mailEnabled=TRUE))
• => Specify how ldap should be asked for groups

LDAP_QUERY_FILTER_ALIAS

• e.g. (&(mailAlias=%s)(mailEnabled=TRUE))
• => Specify how ldap should be asked for aliases

LDAP_QUERY_FILTER_DOMAIN

• e.g. (&(|(mail=*@%s)(mailalias=*@%s)(mailGroupMember=*@%s))(mailEnabled=TRUE))
• => Specify how ldap should be asked for domains

LDAP_QUERY_FILTER_SENDERS

• 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

DOVECOT_TLS

• empty => no
• yes => LDAP over TLS enabled for Dovecot

Dovecot

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

DOVECOT_BASE

• empty => same as LDAP_SEARCH_BASE
• => Tell Dovecot to search only below this base entry. (e.g. ou=people,dc=domain,dc=com)

DOVECOT_DEFAULT_PASS_SCHEME

• empty => SSHA
• => Select one crypt scheme for password hashing from this list of password schemes.

DOVECOT_DN

• empty => same as LDAP_BIND_DN
• => Bind dn for LDAP connection. (e.g. cn=admin,dc=domain,dc=com)

DOVECOT_DNPASS

• empty => same as LDAP_BIND_PW
• => Password for LDAP dn sepecifified in DOVECOT_DN.

DOVECOT_URIS

• empty => same as LDAP_SERVER_HOST
• => Specify a space separated list of LDAP uris.
• Note: If the protocol is missing, ldap:// will be used.
• Note: This deprecates DOVECOT_HOSTS (as it didn't allow to use LDAPS), which is currently still supported for backwards compatibility.

DOVECOT_LDAP_VERSION

• empty => 3
• 2 => LDAP version 2 is used
• 3 => LDAP version 3 is used

DOVECOT_AUTH_BIND

• empty => no
• yes => Enable LDAP authentication binds

DOVECOT_USER_FILTER

• e.g. (&(objectClass=PostfixBookMailAccount)(uniqueIdentifier=%n))

DOVECOT_USER_ATTRS

• 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

DOVECOT_PASS_FILTER

• e.g. (&(objectClass=PostfixBookMailAccount)(uniqueIdentifier=%n))
• empty => same as DOVECOT_USER_FILTER

DOVECOT_PASS_ATTRS

• 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

Postgrey

ENABLE_POSTGREY

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

POSTGREY_DELAY

• 300 => greylist for N seconds

Note: This postgrey setting needs ENABLE_POSTGREY=1

POSTGREY_MAX_AGE

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

Note: This postgrey setting needs ENABLE_POSTGREY=1

POSTGREY_AUTO_WHITELIST_CLIENTS

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

Note: This postgrey setting needs ENABLE_POSTGREY=1

POSTGREY_TEXT

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

Note: This postgrey setting needs ENABLE_POSTGREY=1

SASL Auth

ENABLE_SASLAUTHD

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

SASLAUTHD_MECHANISMS

• 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

SASLAUTHD_MECH_OPTIONS

• empty => None
• e.g. with SASLAUTHD_MECHANISMS rimap you need to specify the ip-address/servername of the imap server ==> xxx.xxx.xxx.xxx

SASLAUTHD_LDAP_SERVER

• empty => same as LDAP_SERVER_HOST
• Note: since version 10.0.0, you can specify a protocol here (like ldaps://); this deprecates SASLAUTHD_LDAP_SSL.

SASLAUTHD_LDAP_START_TLS

• empty => no
• yes => Enable ldap_start_tls option

SASLAUTHD_LDAP_TLS_CHECK_PEER

• empty => no
• yes => Enable ldap_tls_check_peer option

SASLAUTHD_LDAP_TLS_CACERT_DIR

Path to directory with CA (Certificate Authority) certificates.

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

SASLAUTHD_LDAP_TLS_CACERT_FILE

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

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

SASLAUTHD_LDAP_BIND_DN

• 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

SASLAUTHD_LDAP_PASSWORD

• empty => same as LDAP_BIND_PW

SASLAUTHD_LDAP_SEARCH_BASE

• empty => same as LDAP_SEARCH_BASE
• specify the search base

SASLAUTHD_LDAP_FILTER

• empty => default filter (&(uniqueIdentifier=%u)(mailEnabled=TRUE))
• e.g. for active directory: (&(sAMAccountName=%U)(objectClass=person))
• e.g. for openldap: (&(uid=%U)(objectClass=person))

SASLAUTHD_LDAP_PASSWORD_ATTR

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

SASL_PASSWD

• empty => No sasl_passwd will be created
• string => /etc/postfix/sasl_passwd will be created with the string as password

SASLAUTHD_LDAP_AUTH_METHOD

• 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

SASLAUTHD_LDAP_MECH

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)

SRS_SENDER_CLASSES

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

SRS_EXCLUDE_DOMAINS

• empty => Envelope sender will be rewritten for all domains
• provide comma separated list of domains to exclude from rewriting

SRS_SECRET

• 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

SRS_DOMAINNAME

• 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

Default Relay Host

DEFAULT_RELAY_HOST

• empty => don't set default relayhost setting in main.cf
• default host and port to relay all mail through. Format: [example.com]:587 (don't forget the brackets if you need this to be compatible with $RELAY_USER and $RELAY_PASSWORD, explained below).

Multi-domain Relay Hosts

RELAY_HOST

• empty => don't configure relay host
• default host to relay mail through

RELAY_PORT

• empty => 25
• default port to relay mail through

RELAY_USER

• empty => no default
• default relay username (if no specific entry exists in postfix-sasl-password.cf)

RELAY_PASSWORD

• empty => no default
• password for default relay user