Value: [rating=3]
Our commentary: Mark Brownlow's review of Litmus - an inbox preview tool shows the benefits of knowing how your emails appear in different inboxes. It's always been difficult to get emails to render correctly for the main readers. You're very dependent on the skills of your email designer in tailoring their HTML and CSS for Email since it's so different to web design.
Marketing implications: It's particularly you ask your agency to test a new design against all the main email reading platforms listed here.
Increasingly, email service providers like the SmartFOCUS tool we use incorporates email platform preview within the system and make it part of the process of editing and reviewing and email, so make sure you ask the question when you switch providers too.
Recommended link: Email Tool review - review of Litmus