This argues strongly for a "mid:xyzy(_at_)wawa(_dot_)com/cid:wwww@ixi.org"
format
- using slashes to separate the components.
I don't see any positive value to using relative URLs of the form
("../cid:www@ixi.org") to refer to content-IDs when an absolute one
("cid:www@ixi.org") seems like it will do just as well in every
circumstance I can think of. In addition, there's a serious negative:
the same content-ID can occur in multiple contexts, and are actually
the same. If two different MIDs contain the same body with the same
CID, the CIDs are really the same, and
"mid:xyzy(_at_)wawa(_dot_)com/cid:www@ixi.org" creates an unnecessary
distinction.
In fact, "mid:xyzy(_at_)wawa(_dot_)com/cid:www@ixi.org" is quite misleading in
the case where the message is message/external-body, since the content
isn't actually inside the given message at all.