Here is a patch to fix rmail editing problems associated with the
content-type header and reapplying the transfer-encoding to edited
messages.

                                        Ken

* lisp/mail/rmailedit.el (rmail-cease-edit): 
If no content-type in edited headers, look for one in original
headers and add it to edited headers (Bug #26918).
Marker to track start of new body, so that content-transfer-encoding
gets applied only to body (Bug #27353).
Ensure blank line at end of message after encoding, not before.