Looks like Eudora uses the machine's default browser, so that answers that one. At a guess, I'd say the mail client to watch out for when formatting HTML email would be the AOL.
I use Netscape Messenger, out of long time habit. Been thinking about Eudora, but I have little need for auto-filtering etc.
Most of them do punt to a browser Tedster. A couple of newer ones use a seamless approach with just the ie engine (shown right in their window). Pegasus, Agent, and Eudora all launch your default browser (risky).
I think with the proliferation of html/js/browser scripting viruii, most people have wised up and turned off as much as they know how.
I sent a report to a guy in html just yesterday who wrote me back that he would not view html email in any fashion. So I put it on a website...
>What do you and your clients use for their e-mail access?
I'm have a system rube goldberg would be pround of: I use Souper 95 to pull down articles from Hamster mail/news server that pulls down articles from dozens of pop and news servers and then read and reply with Yarn news/email reader (whew). Editing by edit plus, spell checking by "Spell Check" (yes, it's name), and mime/attachment decoding by UUdeview. So, for me to get html/mimed email requires a external program launch. Needless to say, most mimed stuff goes to file 13.
I've yet to find a "modern" setup that can match it for speed and flexibility.