Comment 21 for bug 490935

As I wrote in npm.m-n:
If we want to store internal data in X-headers, we have to make sure that
- all headers must get out of storage *exactly* as they have been put there
- internal headers must not 'leak' to the outside
That way, we could store comments etc. in some X-Mozilla-Comments header that is
only visible to Mozilla itself and would, eg., not be saved when saving messages
to files. (The mbox format already 'escapes' certain lines to work around problems.)

Alas, Mozilla's mbox handling is not 'transparent' in that respect (yet?), see
the empty line problem in bug 141983, bug 67391 and others.