The newly installed bugzilla (3.23.3+?) on b.m.o lets you "tag" bugs <http://www.bugzilla.org/docs/tip/html/query.html#individual-buglists>. Currently it can be used to maintain saved searches by manually adding and removing specific bugs to it. It would be useful for automatic bugmail filtering if the bug's "tags" (i.e. the names of saved searches - at least the static ones) were included in bugmail's contents. E.g. if I added bug N to a saved search named "mdc", the bugmail for that bug would contain "Tags: mdc" in its footer.

I'm not sure this is generally useful enough. Could be done as an extension.