Configuration files syntax

Note: This file is a technical document describing how maddy parses configuration files.

Configuration consists of newline-delimited "directives". Each directive can have zero or more arguments.

directive1 arg0 arg1

Any line starting with # is ignored. Empty lines are ignored too.


Strings with whitespace should be wrapped into double quotes to make sure they will be interpreted as a single argument.

directive0 two arguments
directive1 "one argument"

String wrapped in quotes may contain newlines and they will not be interpreted as a directive separator.

directive0 "one long big
argument for directive0"

Quotes and only quotes can be escaped inside literals: \"

Backslash can be used at the end of line to continue the directve on the next line.


A directive may have several subdirectives. They are written in a {-enclosed block like this:

directive0 arg0 arg1 {
    subdirective0 arg0 arg1
    subdirective1 etc

Subdirectives can have blocks too.

directive0 {
    subdirective0 {
        subdirective2 {
    subdirective1 { }

Level of nesting is limited, but you should never hit the limit with correct configuration.

In most cases, an empty block is equivalent to no block:

directive { }
directive2 # same as above

Environment variables

Environment variables can be referenced in the configuration using either {env:VARIABLENAME} syntax.

Non-existent variables are expanded to empty strings and not removed from the arguments list. In the following example, directive0 will have one argument independently of whether VAR is defined.

directive0 {env:VAR}

Parse is forgiving and incomplete variable placeholder (e.g. '{env:VAR') will be left as-is. Variables are expanded inside quotes too.

Snippets & imports

You can reuse blocks of configuration by defining them as "snippets". Snippet is just a directive with a block, declared tp top level (not inside any blocks) and with a directive name wrapped in curly braces.

(snippetname) {

The snippet can then be referenced using 'import' meta-directive.

import snippetname

The above example will be expanded into the following configuration:


Import statement also can be used to include content from other files. It works exactly the same way as with snippets but the file path should be used instead. The path can be either relative to the location of the currently processed configuration file or absolute. If there are both snippet and file with the same name - snippet will be used.

# /etc/maddy/tls.conf
tls long_path_to_certificate long_path_to_private_key

# /etc/maddy/maddy.conf
smtp tcp:// {
    import tls.conf
# Expanded into:
smtp tcp:// {
    tls long_path_to_certificate long_path_to_private_key

The imported file can introduce new snippets and they can be referenced in any processed configuration file.

Duration values

Directives that accept duration use the following format: A sequence of decimal digits with an optional fraction and unit suffix (zero can be specified without a suffix). If multiple values are specified, they will be added.

Valid unit suffixes: "h" (hours), "m" (minutes), "s" (seconds), "ms" (milliseconds). Implementation also accepts us and ns for microseconds and nanoseconds, but these values are useless in practice.


1h 5m

Data size values

Similar to duration values, but fractions are not allowed and suffixes are different.

Valid unit suffixes: "G" (gibibyte, 1024^3 bytes), "M" (mebibyte, 1024^2 bytes), "K" (kibibyte, 1024 bytes), "B" or "b" (byte).


3M 5K

Also note that the following is not valid, unlike Duration values syntax:


Address Definitions

Maddy configuration uses URL-like syntax to specify network addresses.

Dummy Module

No-op module. It doesn't need to be configured explicitly and can be referenced using "dummy" name. It can act as a delivery target or auth. provider. In the latter case, it will accept any credentials, allowing any client to authenticate using any username and password (use with care!).