"Call to action" is a phrase I've been using quite often, particularly in the domain of mass e-mail. For those of you sending messages with a call to action, rather than information-only or longer, more diverse messages, how do you present this to your users?

Written with Web pages in mind, "Call to Action Buttons: Examples and Best Practices" from Smashing Magazine, covers several best practices for the call to action. Each of these can be applied to mass e-mail. Low clickthrough rate got you down? Work on your call to action.

Major hurdle in applying this to e-mail: image blocking. And don't forget your audience that reads the text part of your message and not HTML (pay extra, special attention for internal communications).