If you are going to get real serious about building a large
infrastructure around search and retrieval of stuff like what you
mentioned, you may want to check out the stuff happening around KQML
(Knowledge Query Manipulation Language). There is a home page at
cs.umbc.edu and there is another at ksl.stanford.edu (and other
places). KQML has been used by Enterprise Integration Technology (home
page at eit.com) for similar (not same) types of integration (with
mail and http).
Good luck
Surf along.
Sankar