sandbox-milter

The purpose of this milter is to trap and redirect certain emails. This is useful for a development environment, where certain emails that are sent out by accident, e.g. to real customers, are redirected to a developer's email address.

sandbox-milter provides both an "smtpd" and "nonsmtpd" milter. The type of milter that is started is determined through a command-line argument.

Prerequisites

• Python 2.7 (provided by the Debian python2.7 package)
• Python milter (provided by the Debian python-milter package)

This milter has been tested with Postfix 2.7 on Debian Linux 7.1.

Example postfix configuration

milter_default_action = accept
non_smtpd_milters = unix:/milter/sandbox_nonsmtpd_milter.sock
smtpd_milters = unix:/milter/sandbox_smtpd_milter.sock
milter_protocol = 6

Note: Postfix is chrooted on Debian by default chrooted, so be sure to keep that in mind when configuring the milter socket paths

Usage

sandbox_milter.py smtpd
sandbox_milter.py nonsmtpd

Output is logged to the mail.info and/or mail.debug syslog facilities

Configuration

The valid_senders file contains a list of legitimate senders whose emails are not redirected iff sent through SMTP.

The allowed_recipients file contains a list of recipients whose emails are never redirected to redirect_address. This usually contains a list of development and test user email addresses. This file can contain both emails and domains (in the form of "@domain.tld").

Neither valid_senders nor allowed_recipients files should contain any comments or anything other than email addresses or domains.

The valid_senders and allowed_recipients files are re-read upon each email delivery, so changes to these two files do not require sandbox-milter to be restarted. The text format that is used in both files causes the milter to not scale well when these two files grow large. Should this be the case, these files should be turned into database or hash files.

Changes to sandbox_milter.cfg will require sandbox-milter to be restarted in order for these changes to take effect.

Rules implemented by sandbox-milter

Redirect email to redirect_address unless:

1. Envelope sender email address is in valid_senders list and email is sent through SMTP, or
2. Envelope recipient email address or domain is in allowed_recipients

Installation

1. Create a milter group, and add the postfix user to it
2. Create a milter user, and assign it to the milter group
3. Copy or symlink sandbox_milter.rc to /etc/init.d/sandbox_milter
4. Execute: update-rc.d sandbox_milter defaults