[exim] OT: Extracting information from an email

Hi All

This isn't strictly about Exim, but there are so many knowledgeable
people on this list that I'm sure someone can point me in the correct
direction. My apologies is this is to far off topic.

I want remote applications to pass information between themselves. The
data will be in XML format (no-brainer these days). For various reasons
the communications link between the two system can not be guaranteed, so
rather than use some direct link protocol I want to send the data via
email. It may be that some human intermediary will be part of the
communications chain too. So the system has to cope with data being
forwarded and the like.

For security reasons I only want to process the email if it was signed
by a known GnuPG key. I don't want to trust the From header as these
are easy to forge.

I plan to set up a pipe delivery from exim to a script I'll write. The
script will need to extract the various mime parts for later processing.
munpack(1) does a nice job of extracting the various mime parts for me,
but I am having a problem validating the email's signature.

At the moment I'm testing this all out by hand using Evolution as my
MUA, but I want the system to cope whatever MUA is used (Evolution,
Outlook, JavaMail, mutt, pine, you name it).

What I'm lacking is a nice guide on how to check signed emails. There
must be a standard, something I'm missing because mutt, Evolution,
Outlook, ... can all interoperate. Can some one please put me out of my
misery and point me at the appropriate documentation.

Thanks
Steve
--
Steve Dobson

I am not an Economist. I am an honest man!
-- Paul McCracken