[Exim] selective relay

OK.. I had emailed yesterday, and I'm much farther along than I was.

I have the following SQL call that will return either an email address or
null:
${lookup mysql{MYSQL_GRABMAIL}}

Now here's my problem. I want to do this lookup in a router and, if i get
an email address, send it to a transport where I manipulate the
to/from/body/etc. If it's null, I want it to fail and eat the email.

I think I need to use manualroute, because won't a redirect router
immediately spit the email out?

Please help,
Erik Jacobs