A pymilter based sendmail/postfix pre-queue filter with the ability to add, remove and modify e-mail headers.
The project is currently in beta status, but it is already used in a productive enterprise environment which processes about a million e-mails per month.

The basic idea is to define rules with conditions and modifications which are processed when all conditions are true.

Dependencies

Pymodmilter is depending on these python packages, but they are installed automatically if you are working with pip.

Installation

Install pymodmilter with pip and copy the example configuration file.

pip install pymodmilter
cp /etc/pymodmilter/pymodmilter.conf.example /etc/pymodmilter/pymodmilter.conf

Modify /etc/pymodmilter/pymodmilter.conf according to your needs.

Configuration options

Pymodmilter uses a configuration file in JSON format. The options are described below. Make a copy of the example configuration file in the docs folder to start with.
Rules and modifications are processed in the given order.

Global

The following global configuration options are optional:

socket
The socket used to communicate with the MTA.
local_addrs
A list of hosts and network addresses which are considered local. It is used to for the condition option local. This option may be overriden within a rule object.
log
Enable or disable logging. This option may be overriden by a rule or modification object.

Rules

The following configuration options are mandatory for each rule:

modifications
A list of modification objects which are processed in the given order.

The following configuration options are optional for each rule:

name
Name of the rule.
conditions
A list of conditions which all have to be true to process the rule.
local_addrs
As described above in the Global section.
log
As described above in the Global section.
pretend
Just pretend to make the modifications, for test purposes.

Modifications

The following configuration options are mandatory for each modification:

type
Set the modification type. Possible values are:
- add_header
- del_header
- mod_header
- add_disclaimer

The following configuration options are mandatory based on the modification type in use.

add_header
- header
  Name of the header.
- value
  Value of the header.
del_header
- header
  Regular expression to match against header lines.
mod_header
- header
  Regular expression to match against header lines.
- search
  Regular expression to match against the value of header lines. You may use subgroups or named subgroups (python syntax) to include parts of the original value in the new value.
- value
  New value of the header.
add_disclaimer
- action
  Action to perform with the disclaimer. Possible values are:
  - append
  - prepend
- html_template
  Path to a file that contains the html representation of the disclaimer.
- text_template
  Path to a file that contains the text representation of the disclaimer.
- error_policy
  Set what should be done if the disclaimer could not be added (e.g. no body text found). Possible values are:
  - wrap
    The original e-mail will be attached to a new one containing the disclaimer.
  - ignore
    Ignore the error and do nothing.
  - reject
    Reject the e-mail.

The following configuration options are optional for each modification:

name
Name of the modification.
log
As described above in the global object section.

Conditions

The following condition options are optional:

local
If set to true, the rule is only executed for e-mails originating from addresses defined in local_addrs and vice versa.
hosts
A list of hosts and network addresses for which the rule should be executed.
envfrom
A regular expression to match against the evenlope-from addresses for which the rule should be executed.
envto
A regular expression to match against all evenlope-to addresses. All addresses must match to fulfill the condition.

Developer information

Everyone who wants to improve or extend this project is very welcome.