Sometimes for testing purposes you need to save all messages going through Postfix active queue. There are a couple of ways of doing this.

The simplest method is to simply add the “always_bcc” option to the main.cf. This will cause Postfix to send a blind copy of every message to the pre-defined “catch-all” address. A more advanced take on this approach is to create a new domain specifically for BCC mail. The new domain will be defined using sender_bcc_maps and recipient_bcc_maps with regular expressions for more granular control over what is being BCC’d and where. For example, you can add this to main.cf:

sender_bcc_maps = regexp:/etc/postfix/bcc_sender_domains
recipient_bcc_maps = regexp:/etc/postfix/bcc_recpipient_domains

Then you create bcc_sender_domains and bcc_recpipient_domains to BCC all incoming and outgoing mail to/from the same username on the BCC domain:

/^([^@]+)\@primarydomain\.com$/    $1@bccdomain.com

A different approach is to simply copy everything in /var/spool/postfix/active to an archive location in real time. There are several utilities that allow you to do this. The one I use is lsyncd. You will need lsyncd version 2.1.4 or newer. Check out this article on the basics of lsyncd installation and configuration. Here’s a more specific example of the /etc/lsyncd.conf specifically for the purpose of saving Postfix active queue:

settings {
        logfile = "/var/log/lsyncd/lsyncd.log",
        statusFile = "/var/log/lsyncd/lsyncd.status",
        nodaemon = false,
        maxDelays = 3,
        onStartup = true,
        onAttrib = true,
        onCreate = true,
        onDelete = false,
        onModify = true,
        onMove = true,
        delete = false,
}

sync {
        default.rsyncssh,
        delete = false,
        source = "/var/spool/postfix/active/",
        host = "remote_server",
        targetdir = "/target_home/active/",
        delay=3,
        rsync = {
                        owner = true,
                        perms = true,
                        checksum = true,
                        compress = false,
                        acls = true,
                        verbose = true,
                        _extra = {"-Kx"},
        }
}

The “delete = false” option will ensure lsyncd will not remove anything from the target directory. However, as you may imagine, after a period of time you may end up with a huge number of files on the <target_server>. Here’s a simple script that will monitor the target directory and, as soon as the number of files reaches 5,000, the script will move them to a subfolder with the current Unix epoch time:

#!/bin/bash
find /target_home/var/spool/postfix -maxdepth 1 -mindepth 1 -type d | sort -u | while read line
do
if [ `\ls "${line}" | wc -l` -gt 5000 ]
then
	d=$(date +'%s')
	mkdir -p "${line}/${d}"
	find "${line}" -maxdepth 1 -mindepth 1 -type f -exec /bin/mv -f {} "${line}/${d}/" \;
fi
done

Just add that to a crontab to run, say, every half hour for a moderately busy mail server.