Messages can be inserted with C-c C-i (mh-insert-letter).
This command prompts you for the folder and message number, which
defaults to the current message in that folder. It then inserts the
messages, indented by mh-ins-buf-prefix (‘> ’) unless
mh-yank-behavior is set to one of the supercite flavors in
which case supercite is used to format the message. Certain
undesirable header fields (see
mh-invisible-header-fields-compiled) are removed before
insertion.
If given a prefix argument (like C-u C-c C-i), the header is left intact, the message is not indented, and ‘> ’ is not inserted before each line. This command leaves the mark before the letter and point after it.