mail-header-parse-content-type
mail-header-parse-content-type is an alias for `rfc2231-parse-qp-string' in `mail-parse.el
'.
(mail-header-parse-content-type STRING)
Parse QP-encoded string using `rfc2231-parse-string'.
N.B. This is in violation with RFC2047, but it seem to be in common use.