Testing email blasts before they go out is an essential step in any email marketing campaign. Because of the different email clients and services that people use, an HTML email can look very different, depending on the software that reads it. The problem arises when an organization must test a single email across various platforms and operating systems. One solution is to test-send the email to recipients that represent all of the platform and operating system combinations. However, like many errors in email deliverability, it's impossible to account for every situation. So usually, the best you can do is test the email in the major clients and operating systems.

Most email blast services like Vertical Response allow you to send test blasts to a user-defined list of email addresses. This allows you to get real feedback from actual recipients of the email. There are also services that will "preview" what your email will look like in major clients all at once, so you don't need to send test emails to each different email provider. Some examples include CampaignMonitor, PreviewMyEmail.com and Litmus. They charge for the full-featured use of their service and many people (especially nonprofits) find their use unnecessary and expensive. However, they may be a good option for some organizations that consistently send out email blasts to a large number of service providers.

The long and the short of it is that your choices are either 1. free and cumbersome, sending out to test recipients, or 2. expensive and easy, using an email previewer.

For more resources, check out these links:
* http://socialsourcecommons.org/toolkit/show/863