message signature types

[auto15963931]

If this is the wrong place to ask, please point me in the right
direction. Where can I learn more about importing, if such a thing is
even done this way, and making use of message signatures which utilize
an "smime.p7s" file? I got a message from someone who uses this, and I
need to learn about verifying and downloading from a keyserver files
like this. Especially important for me is learning how to check whether
it had been revoked, etc.  Where is a support group for this sort of
signature if this is not it? Thanks.