In my corner of the world, mails are usually written with 8859 (or perhaps utf8) character sets and a low percentage of non ascii codes. Real MUAs seem to prefer qp encoding for themessage text as well as any headers requiring non ascii (display names in From and To, as well as Subject) With qp these headers are still readable without any specific programs. As far as I can tell from my inbox, any mails using 8859 and base64 seem to be spammy - in particular those where there was no need to encode at all
Wolfgang Hamann