I said "handle". Especially Unix programs almost always have a way of going beyond a programs limitations. Elm and pine support mailcap files. IIRC (n)mh does

I said "handle". Especially Unix programs almost always have a way of going beyond a programs limitations. Elm and pine support mailcap files. IIRC (n)mh does as well via mimeview (or is that only the GNU version?). But a program where scripting is a part of its core design, there will certainly be ways of calling an external program for converting HTML to be viewed. Mail and mailx, do they even support mime types? AFAIK they don't but then you just need to set up PAGER with an intelligent enough program I guess. Now if you said telnet or netcat, I would truly have been at a loss.