PHP Sendmail Administration Application

I have a sendmail server and apache webserver. After a domain has been set up I would like the owner of that domain to be able to set up email accounts for that domain. I will, of course, need overriding administration rights as well.

Does anyone know of an open source (preferably) PHP application that can handle the creation and administration of sendmail accounts, with access rights limited by domain?

Even partial scripts would be helpful, if I need to write my own.

SMB