You should create a cron job that expires your database from
time to time.

This cron job should call couriergrey with the arguments "-e 365" to
expire entries, that are older than one year. Make sure that couriergrey
is run as the user, that normally accesses the database. E.g. on a
standard Debian system this is the user 'daemon'.

On a Debian system, create the file /etc/cron.weekly/couriergrey with
the following content:

===[snip]===============================================================
#! /bin/bash

su -c "/usr/bin/couriergrey -e 365" daemon
===[snip]===============================================================
