mh-position-on-field
mh-position-on-field is an autoloaded Lisp function in `mh-letter.el
'.
(mh-position-on-field FIELD &optional IGNORED)
Move to the end of the FIELD in the header.
Move to end of entire header if FIELD not found.
Returns non-nil if FIELD was found.
The optional second arg is for pre-version 4 compatibility and is
IGNORED.