How can I solve this problem?

Hi,

I'm running ezmlm-0.53-idx-0.41 and I've run into an odd situation that I need 
help with.

I blame this on an exchange server, but that doesn't help fix the problem.  
The mailing list that I'm referring to allows members to post messages, other 
messages go to the moderator.  

All e-mail messages from one user who is correctly subscribed to the list, 
come to the moderator.  I'm guessing what is causing the problem is that the 
user's e-mail address has upper case letters in it.  Is this a possible 
problem?  If so, how can I fix it? 

Thank you,

Mark Neidorff