This plugin will add a task which will run on a daily basis to prune/delete automatically the old personal conversations at your forum, which have not had a reply since a certain amount of time. By default it is set to 1 year, but you can change it to suit your needs.
And as last, but certainly not least, you can exclude old personal conversations started by members of certain groups from being prunned automatically.
As mentioned above, the time criteria is based on conversation 's last reply time. If you would like to base it on the start time instead, that is no problem. It is a small edit which I can made it for you and send you the modified file.
If you have any presale questions regarding this plugin, please do not hesitate to ask in the support topic or contact me in private.