[exim] Queuing only deliverable messages for mailscanner

I am using mailscanner/spamassasin to scan all my incoming mail. All mail
is queued via the "queue_only" option, scanned by mailscanner then delivered
via another exim4 process. What I would like to do is somehow verify the
local recipient address before putting it in the queue for scanning. In
other words I'd like the following logic:

If the message is from a host allowed to relay then queue it for scanning
(This handles messages from my clients to outside addresses)
If the message is to a valid local address queue it for scanning (This
handles messages to valid_users@???)
If the message is to an invalid local address, bounces it immediately (This
handles messages to invalid_users@???)

The whole purpose being to not waste CPU time scanning messages that I KNOW
will be bounced anyway.

Does this make sense and is it possible?

Robert B. Brown, II
IT Director
Foxcroft Academy
robert.brown@???
Voice: 207-564-8351
Fax: 207-564-8394
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