From mrose(_at_)dbc(_dot_)mtview(_dot_)ca(_dot_)us Wed Jan 20 12:17:54 1993
Content-ID: is used when referencing external body parts so you can do
caching correctly. This means they have to be globally unique.
That's an interesting use of Content-ID; of course you could do a better job
of caching if you kept a record of external-body parameters, instead.
Anyway, it's stretching things to imply that's an intended use of Content-IDs.
Bottom line: if it isn't broken, don't try to break it.
Yeah, I wasn't aware of any implementations that counted on global uniqueness
(do you mean that MH 6.8 uses the above hack?). I was just trying to use
them in the way the RFC suggests, and found them awkward, but not unusable.
Jay