Milter are script executed by postfix upon sending or receiving an email.
We use this system to allow pagure's users to comment on a ticket (or a pull-request) by directly replying to the email sent as a notification.
Pagure's milter is designed to be run on the same machine as the mail server (postfix by default). Postfix connecting to the milter via a unix socket.
The milter itself is a service managed by systemd.
You can find all the relevant files for the milter under the milters folder
in the sources.
The first step to enable the milter on a pagure instance is thus to install the
.service file for systemd and place the corresponding script that, by
default, should go to /usr/share/pagure/comment_email_milter.py.
If you are using the RPM, install pagure-milters should provide and install
all the files correctly.
Make sure the milter is running and will be automaticall started at boot by running the commands:
To start the milter:
systemctl start pagure_milter
To ensure the milter is always started at boot time:
systemctl enable pagure_milter
To actually activate the milter in postfix is in fact really easy, all it takes
is two lines in the main.cf file of postfix:
non_smtpd_milters = unix:/var/run/pagure/paguresock smtpd_milters = unix:/var/run/pagure/paguresock
These two lines are pointing to the unix socket used by postfix to communicate
with the milter. This socket is defined in the milter file itself, in the
sources: milters/comment_email_milter.py.