Our default Postfix configuration can easily be extended to add parameters or modify existing ones by providing a docker-data/dms/config/ This file uses the same format as Postfix does (See official docs for all parameters and syntax rules).


One can easily increase the backwards-compatibility level and set new Postscreen options:

# increase the compatibility level from 2 (default) to 3
compatibility_level = 3
# set a threshold value for Spam detection
postscreen_dnsbl_threshold = 4

How are your changes applied?

The custom configuration you supply is appended to the default configuration located at /etc/postfix/, and then postconf -nf is run to remove earlier duplicate entries that have since been replaced. This happens early during container startup before Postfix is started.

Similarly, it is possible to add a custom docker-data/dms/config/ file that will override the standard Note: Each line in this file will be passed to postconf -P, i.e. the file is not appended as a whole to /etc/postfix/ like docker-data/dms/config/! The expected format is <service_name>/<type>/<parameter>, for example:

# adjust the submission "reject_unlisted_recipient" option


There should be no space between the parameter and the value.

Run postconf -Mf in the container without arguments to see the active master options.