Multiple Identities in Outlook Express

One of my users is using Outlook Express v6.0. She has 2 identities using two different email servers, a local broadband provider and a small website hosting service. Occassionally, when she sends an email from one account, the reply for some reason comes to the other account. This makes it very difficult to keep straight which email goes to which identity. Another point that may help is that she is using the free version of MailWasher to help with Spam. Any help would be greatly appreciated.