Add header to outgoing email with postfix

Question

Can someone please provide an example on how to add a

Precedence: bulk

header to all outgoing emails using postfix.

I would like to know what file(s) to create or edit and what I should put in them. And also what to do to make postfix read in the new configuration.

I have read quite a bit of documentation but it seems to expect a high level of familiarity with postfix. All I have gathered so far is that it may have something to do with /etc/postfix/main.cf and somehow add a PREPEND statement.

Note that mucking about with postfix (and email in general) is way out of my comfort zone.

Answer 1

Unfortunately, this isn't super straightforward in postfix, but certainly doable.

/etc/postfix/main.cf, set header_checks to:

header_checks = regexp:/etc/postfix/my_custom_header

Then create /etc/postfix/my_custom_header and put this regular expression in it:

/^Content-Transfer-Encoding:/i PREPEND Precedence: bulk 

Then restart postfix - depends on your distro, but most likely you can restart it with service postfix restart or /etc/init.d/postfix restart.

Thats about it. What this does is that postfix will find the Content-Transfer-Encoding: header in the email and add your Precedence: bulk line right before it, hence the PREPEND action.

Now, this assumes that the Content-Transfer-Encoding header actually exists in the emails. You may want to take a look at the headers on a typical outgoing email and find a good one to match upon. You can get crazy with the regex to suit your needs.