Exchange 2000 and Outlook Express

[Marta]

My customer has a problem: when he sends a mail using "Outlook Express" to another user which has a mailbox in the same Exchange 2000 Organization, the person who receives the mail does not see in "from" what the sender has configured in "display name" of his account in Outloo Express; what he sees is the display name of the mailbox.
In Exchange 5.5 this does not happen, you can write what you want in Outlook Express and this is what you see when you receive a mail from this person.
Do you Know if this is the standard behaviour???????
Please, help me.
Thank you very much.