email header checker

Question

Hi there,

I'm looking for a solution to track which email clients are my subscribers using (outlook 2007, outlook 2003, thunderbird, gmail).

I can only think of using a 1px tracker to be embedded in the email and whenever the email gets opened it does a http get request for the image. This way, i should be able to capture some info like this on my access.log

203.123.456.78 - - [18/Oct/2010:08:50:13 +0000] "GET /images/more_results.jpg HTTP/1.1" 304 0 "http://subdomain.domain.tv/category?page=3" "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; .NET4.0C; .NET4.0E)"

However, is this approach able to track the email platforms used? I appreciate any suggestion or feedback. :D