Misdelivered messages

[Dana Canfield]

In the past week or so, we've had trouble with spam being delivered to 
the wrong recipients.  It's difficult to explain, so I'll use an example:

hackxx at uindy.edu and xxmelser at uindy.edu are local users receiving 
hundreds of spam per hour.  None of it is addressed to them.  Their 
email addresses don't appear anywhere in the message source.  The 
messages in hackxx's account appear to be the same messages that 
xxmelser is receiving.  Most of the misdirected messages seem to be 
addressed to other local users, such as xxmilton at uindy.edu or 
foxworthxx at uindy.edu. 

To further confuse the issue, this only happens with spam.  A legitimate 
message mailed to xxmilton at uindy.edu goes through to xxmilton's account 
and doesn't appear in the other users' mailboxes.  The *only* clue I 
have found is that most of these spams that get misdirected have a gap 
between the To: and the address in the message header, like this:
To:           <foxworthxx at uindy.edu>

Does anyone have any clue what might be going on here?

Thanks
DC