% 9p read mail/mbox/40/raw |grep -i '^content'
Content-Type: text/plain; charset=
Content-Transfer-Encoding: 8bit

Does it mean that the character set is in iso-8859-15 but the sender
of the message somehow set it wrongly in the headers to be iso-8859-1?
Hence mailfs is failing at trying to convert it from iso-8859-1 to utf-8
because it trusts what's written in the headers?

Thanks,
Mathieu.