During my investigations, I came across the below information on TechNet...
Exchange Server 2010 introduces the shadow redundancy feature to provide redundancy for messages for the entire time they're in transit. The solution involves a technique similar to the transport dumpster. With shadow redundancy, the deletion of a message from the transport databases is delayed until the transport server verifies that all of the next hops for that message have completed delivery. If any of the next hops fail before reporting back successful delivery, the message is resubmitted for delivery to that next hop.
By default in Exchange 2010, Receive connectors delay SMTP acknowledgement when receiving messages from systems that do not support shadow redundancy, for up to 30 seconds. (The Equitrac Scan to Me does not support shadow redundancy, hence the delay).
To remove the 30 second delay on these emails, I needed to set the 'MaxAcknowledgementDelay' on the Receive connectors to 0, effectively disabling it.
To do this, in Exchange Management Shell (PowerShell), I ran
Set-ReceiveConnector "connector name" -MaxAcknowledgementDelay 0
Emails from the MFD are now sending instantly with no delay.
In the event that you need to revert back to the default of 30 seconds, run
Set-ReceiveConnector "connector name" -MaxAcknowledgementDelay 00:00:30