Thanks for the suggestion, but there is no black/white listing. I did have a message rule for the sender (to direct his incoming emails to a separate sub folder), but the same problem occurred after I deleted the rule and his messages just went to my Inbox.

Finally, There isn't substitution of a separate attachment nor any message even telling me that the attachments had been deleted. In fact, I originally thought that he just forgo to attach them!

I have no idea what else to try.....