No, it's a binary plist in disguise
😡 You can get a less weird format by saving as a "web page, complete" from Firefox (but if what you need really is a Tiger-style webarchive, you're going to need Safari 2.0).
It might be a good idea to back up a little here. Are you working from
this tip? That's really for Tiger anyway, I wouldn't count on it working with earlier versions of Mail.