Happy New Year to you, Peter.
Is you mail client Outlook Express ?
I don't know if this applies to you, but I have a feeling that with OE, if you have one address iin the "To" box and others in the "cc" or "bcc" fields....only the primary addressee will get the receipt request
The recipients can set their mail client to ignore a receipt request, but that should not prevent the request from getting through to them.
I'm off to check out my idea.....saw it posted somewhere if only I can find it again