While we spend a lot of time as designers worrying about rendering in the desktop email clients, and quite rightly, it's sometimes easy to forget about the growing use of web based email clients.

Particularly as offerings like Yahoo Mail (and recently Gmail) offer IMAP capabilities, more and more people will be accessing their email in part of completely through a web browser.

Over at Email Marketing Reports, Mark Brownlow has recently updated his Email and webmail statistics article with recent numbers. Yahoo cites a staggering 543 million webmail accounts, of which Yahoo provides almost half.

What does this mean for web designers? It means that testing in webmail clients is even more important than ever. Even though your subscribers are probably using one of the major browsers to view their email, different webmail providers render your newsletters in different ways.

You might want to set yourself up with free accounts for Yahoo, Hotmail and Gmail at least, and test with them. Also, check out the new design and spam testing tool over at Campaign Monitor that can save you a lot of time.