Read receipts return to a different email account

I have what seems to me to be a VERY bizarre problem. I have a Mac Mini, run OS 10.7.3, Mac Mail 5.2(1257). Just set up the new Mac Mail version on my Mini though I had used a different version in the past. I have two email accounts set up - one is an Exchange account and the other is a POP account. Yesterday, I sent out several emails from the Exchange account. Within a few minutes, read receipts began coming back to me. This was slightly strange since I didn't know Mail was set up to ask for Read receipts. But what is MUCH STRANGER (to me, at least) is that the read receipts ALL get sent back to the POP account email address even though the messages are being sent from the Exchange account address. I've sent multiple messages from the Exchange account now and the read receipts reliably return to the POP account. This does NOT occur when I send email from the Exchange account on Mac Mail on my laptop. Can someone tell me what is going on?

First, how do I get rid of the read receipts function (I don't really want it)?

Second, what the **** is going on with the routing of the read receipts?

Thanks

Jon