Zoho provides a standard view for "Customer Viewed" invoices.

What would be more useful would be the opposite: "Customer Unviewed" Invoices, because those are the ones likely to need follow up (invoice went to spam folder, etc).

There is a field, "Customer Viewed Time", but this does not seem to work, because it seems to test empty for all viewed and unviewed invoices.  Is this a bug?  Does someone have a solution?

Thanks