Procmail split mailing list answer

Question

The common ethicete about mailing lists is to answer to a human, and CC the mailing list, like this:

To: help-volounter@dev.full
Cc: some-program@mailing-list.com
Subject: Re: Describtion of the problem

Problem is that I get two copies of such email(it's expected). I would like to procmail one copy to mailing list mbox, and another to inbox mbox. Is it simple way to do it?

Answer 1

It's not entirely trivial, but there are some building blocks you may find useful.

You can detect whether you have already received a message by keeping a cache of seen message-id:s. This is a standard technique described in the procmailex man page in more detail. I would propose to use the same technique to decide where to file an incoming message; if it has not been seen before, deliver to your inbox; otherwise, file to the list's folder.

The locking becomes somewhat more complex because you need to obtain the lock file before entering the formail -D recipe. This can be done by using the LOCKFILE special variable.

# Is this message addressed both to yourself and to the list?
:0
* ^TO_you@example\.net\>
* ^TO_mailing-list@elsewhere\.example\.org\>
{
    # Select regular inbox as default target for this message
    dest=$DEFAULT

    # Lock msgid.lock for exclusive access to msgid.cache
    LOCKFILE=msgid.lock

    # If message-id is already cached, override $dest
    :0
    * H ? formail -D 8192 msgid.cache
    { dest=listbox/ }

    # Release lock
    LOCKFILE=

    # Deliver to $dest
    :0
    $dest
}

This is not 100% foolproof. If you get a Bcc:, for example, your own address will not be in the headers, and so ^TO_ yourself will not match.