Interact - Duplicate Emails

Use Case

We have multiple "Support" mailboxs at hachette for one of our Publishers. We have build some Outlook macros to format incoming emails and push them to Interact to be logged as Requests. This works and is fine.

The issue lies when a user emails multiple support boxes for the SAME query (i.e. they just want a quick reply). Currently our Outlook Macros will forward to every email and interact will log each email as one Request. So if a user emails 3 Support mailboxes there will be 3 Requests (2 being duplicates).

My idea was to extract the MessageId from the header which is unique for all of the emails (even though they are delivered to different mailboxes) and store this against each Request that comes in. The idea was in Interact was to use FindObject to check to see if the Request already exists with that MessageId (im storing the email MessageId in our $C_ExternalSystemId field). Example:

FindObject('EnhancementRequest',$C_ExternalSystemID,RequestedMsgID) = null

Now the Interact rule doesnt find any duplicates because I'm presuming the transactions are being processed at the same time, so there isnt a transaction to query. Which is fine.

I thought about creating a WORKFLOW on record creation to check, but i see that FindObject method doesnt exist for Business Rules/Workflows.

Is there any other method of locating existing records I could use?