This may or may not help... perhaps the person sending you the email has sent
it to two different email addresses that you own and one account is set to
automaticly forward emails to the other account.... Its a long shot i know
but this happened to me a little while ago.
I appreciate you both taking the time, but I managed to sort it in the end.
For some reason I had 2 e-mail accounts both with the same details, so they
both downloaded the mail. Silly me!! Thanks once again.