When trying to open the sendmail.src.rpm file (ie. press enter on it) (tried a few others, only worked with this one ...), mc runs elm (and doesn't open the rpm archive) ... I edited the bindings file and commented out the elm part. Worked afterwards. (file correctly recognizes the file as RPM)
Just noted that this seems to every *mail* rpm package (however, touching an empty file mymail.rpm or something similar is not enough ...).
weird I can't figure out why it is treating those files as a mail file. I just removed the mail entry, as it's fairly pointless, anyway.