I originally created this back in 2004 or so for my hosting company, and then released it as open source on riaforge in 2012/13.
This handy custom extension for your ColdFusion administrator will automatically respool your failed mail every x minutes/hours until the file is [x] hours old, if it still has not delivered then it will be deleted.
This module for WHMCS allows you to send on demand or automated monthly account statements to your customers showing them which invoices they have outstanding. A feature still sorely lacking from WHMCS.
Once upon a time I used to own a web hosting company, we used the HELM hosting control panel. Once the software became defunct I needed a way to migrate the customers to a new system called WHMCS. No such system existed, so I wrote my own.