Sue not unless the sender requested a read reciept and the recipient didn't trap it from returning. Also if it was an html mail (with an inlined image) you can check the server logs and see if that image was accessed or not. lastly, you could try to get a record of the server logs from the recipient's host and see if they downloaded that piece of mail from the mail server but the chance of actually getting that log is closer to none then it is to slim.
We'll be moving a few more services from this server this coming weekend to help prevent the overload closed messages, FYI.
