Being a fan of Firefox I gave Mozilla’s Thunderbird a try today. Granted, it’s a lot lighter than Outlook (currently using 2007), but… perhaps it’s too light. Yes, there are plug-ins to augment functionality and features, but..
Perhaps the biggest thing that bugged me about it was the lack of an option to set images from all remote sites to load by default. I realize it’s perhaps not a "safe" thing to do, or that it might increase the amount of spam, but the fact that I always have to click on "Load Images" to load the embedded images slows down processing emails. Emails arrive from so many domains/senders that setting a specific sites on the image-loading-whitelist doesn’t cut it.
I’ll give it another try later.. and if I happen to have missed a setting to set remote images to load by default (I couldn’t find anything on the topic by quick Googling, either), please write a comment.