Email user reply address is wrong is this on the user end or the recipient end

I have a user that is setup on Google apps using their domain but when they send emails to some people when they hit reply another email address comes up ..... I just had the user email me and I hit reply and it shows and went to the correct address ..... Do you think this problem is on those few users end such in their contacts ... or is it the in the email account ... I just log into the google admin panel and look at the account and I don't see a reply address ....any suggestions