With, I assume, pre-formatted html, as in:

http://kerneltrap.org/mailarchive/openbsd-misc/2007/12/10/486713

the email is cut off on the right side by the navigation bar on the right, making the quoted email unreadable. I see a lot of sites and especially blogs totally make posts unreadable for this reason.

I guess one answer is to make sure a horizontal scroll bar is available, which I find not UI sane. (scroll-right, scroll-left, scroll-right,scroll-ad nauseam)

I guess, just make the text flow... and have a link to the source.