Mailgun is advertised as "The Email Service For Developers", allowing you to send 10,000 emails for free every month. It has a nice API, and is very simple to use. A common problem that many ColdFusion developers have, when writing an app, is having access to an SMTP server solely for development practices. You can setup a local server, use some Windows SMTP service, or traffic mail through your personal accounts, but it really is better to have a sandbox that's a bit more separated, for security, sanity, and other reasons. ColdFusion 10+ have a built in SpoolMail utility (based loosely on Ray's project), but sometimes you just need to see the real output in a mail client instead of the browser.
Setting up an account was easy on Mailgun. Right from the homepage was a link to the free sign up page. Once the account was created I was given a Mailgun Subdomain. This is my sandbox to play in, so I clicked on the domain name, for the domain admin page, then clicked on the "Manage SMTP Credentials" link on the "Default SMTP Login" line item. From this page I was able to create a new sender (you can use the default if you wish, but sometimes I'll setup separate addresses for specific tracking purposes).
The final stage is to put the settings in the ColdFusion Administrator. From the mail settings area I entered my new "sender" address as my SMTP server username, the password that I created with the account, set the SMTP server address to "smtp.mailgun.org", and changed the SMTP port to 587. (The default port 25 will NOT work, but 587 with no other settings changes will work fine.)
Now I can send mail with ColdFusion from my dev environment without having to load my own SMTP server or subbing out my personal addresses.