Read Receipts are not processed or only very slow. How to trigger processing manually?

I have sent an e-mail to a large receipient list.  Most is inhouse. The receipients use Outlook 2003, too.

I requested read receipts which I am getting in actually. I have set that the processed receipts are being moved to deleted.

Those read receipts seem to be processed very slow and for some I have the feeling they are not processed at all. They just keep hanging in the inbox.

Can I trigger the processing of the read receipts manually? I would like to be able very fast to tell who has read the e-mail. I am aware that some may decline to sent the receipt but most actually do send a receipt.

Thanks.