I got an email yesterday about a new tool developped by the folks behind Litmus (a tool that shows you what your email will look like in different browsers). The new tool is called Fingerprint and it shows you which email clients your readers are using. I tried it out when I was sending out the newsletter for the Email Marketer's Club yesterday and I was very impressed with the results.
Basically what happens is that you get a piece of code (an image tag) to add to your email and about an hour after sending your campaign you get to see the first results.
I would advise everyone to try it out to get a better idea of which email clients you should be designing your emails for. Is Lotus Notes used by a big part of your audience? Do they use version 6 or 8? Do they use Gmail in Firefox or in Internet Explorer? Do they view your email on their iPhone...
Drop everything you're doing and check it out now! Really. I'm not kidding.
And in case you're wondering: I didn't get paid to post this. I really believe in this product and I think they are selling it way too cheap, so you want to get in and start using it before they realize what goldmine they are sitting on ;-)