Do you send out an HTML newsletter? How many times have you (quite literally) pulled your hair out trying to get it to look the same (or even decent) in different email clients? It's usually a giant guessing game to try and figure out what elements work in what clients.

Guess no more! The folks at Campaign Monitor, makers of an e-newsletter tool, have done the research and provided a nice, comprehensive guide to what you can and cannot do in the major email clients - both off and online!