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About This Manual

This is the Reference Manual for the KumoMTA SMTP server, version 1.0, through release 1.0. For license information, see the Legal Notices.

Because this manual serves as a reference, it does not provide general instruction on SMTP or email infrastructure concepts. It also does not teach you how to use your operating system or command-line interpreter.

The KumoMTA Software is under constant development, and this Manual is updated frequently as well.

If you have questions about using KumoMTA, community support is available in the Forum and the Community Discord.

Typographical and Syntax Conventions

This manual uses certain typographical conventions:


This is a noteworthy section


This indicates a warning


This indicates something that can have dangerous consequences

Text in this style indicates input that you type in examples.

Text in this style indicates the names of executable programs and scripts, examples being kumod (the KumoMTA server executable).

Text in this style is used for variable input for which you should substitute a value of your own choosing.

Text in this style is used for emphasis.

Text in this style is used in table headings and to convey especially strong emphasis.

Text in this style is used to indicate a program option that affects how the program is executed, or that supplies information that is needed for the program to function in a certain way. Example: “The --policy option tells the kumod server the path to the initial policy file to execute on startup”.

File names and directory names are written like this: “The simple-policy.lua file is located in the /etc/kumod directory.”

Character sequences are written like this: “To specify a wildcard, use the ‘%’ character.”

When commands or statements are prefixed by a prompt, we use these:

$> type a command here
#> type a command as root here
kumo> type a KumoMTA CLI command here

Commands are issued in your command interpreter. On Unix, this is typically a program such as sh, csh, or bash.

!!! When you enter a command or statement shown in an example, do not type the prompt shown in the example.

In syntax descriptions, square brackets (“[” and “]”) indicate optional words or clauses. For example, in the following statement, --user is optional:

kumod--policy simple-policy.lua [--user] someuser