Mailer.cfc is, in part, an abstraction for cfmail. While cfmail is already a great encapsulation of email functionality, Mailer.cfc provides several advantages - especially if you are using CFCs.
The first advantage is that it you can pass Mailer.cfc into a component instead of several email-related settings. This is especially useful if you may or may not use a username/password to send email as it keeps you from having to code that conditional into your component.
More significantly, however, is that like DataMgr, Mailer.cfc comes with a "Sim" version that can be used for development and testing. Switching between the two requires no change to your code except on the instantiation of your component. This allows you to test your code without actually sending email.
Mailer.cfc can also log all of the email that it sends in a database table (this feature requires DataMgr, but Mailer.cfc can be used without anything else if you don't use logging).
The use of Notices in Mailer.cfc is also helpful, but beyond the scope of this entry.
Mailer.cfc is open source and free for any use.