Each mail messages has multiple time stamps.  You can see these in File,
Properties, Details.

When you look at the list of messages in Microsoft IE3 Internet Mail or
IE4+ Outlook Express, the Received time is when the message was received
by your ISP's mail server.  The server supplies the time.  This is the
first of possibly several "Received:" lines in the message header.  Each
mail server that a message passes through adds its own Received line.
These are in reverse order, so that the last one listed is the first
server that received the message from the sender.

When you open or print a message, the time displayed is from the
sender's PC when he wrote the message, not when he transmitted it.  The
time comes from his PC.  This is the "Date:" line in the message header.

So if it's the top most Received header with the wrong date, it's a
problem at your mail server.

If it's the Date header that's wrong, then it's the sender's fault.
It's not unusual for these to be wildly off, especially for spam or
viruses.