I've been using fetchmail to retrieve mail from my ISP and feeding it to courier using the option: mda "reformime -r | /usr/sbin/sendmail %T"

I've found that in most cases, this will allow most of the mail from my ISP, including all of the badly formatted, nasty spam and mailings from bn.com, to be delivered using courier. However, occasionally there are messages that reformime processes and courier still doesn't accept. The attached is an especially interesting case, since the original message will be delivered by courier, but the output of reformime -r will be rejected as not having proper MIME headers.