Not entirely how to do it Outlook exprees, but in outlook  you can determine
two things:

1. Your user info:
go to tools/ options and adjust your user info as a part of the email
account setup information (the place where you input the smtp / pop3 server
etc.

2. when you are sending an email message go to options from the email window
and there should be an option called ''direct replies to"

Let me know if that makes sense. That'll at least give you something to
search for in the help section of outlook express.

I don't use express otherwise I would be more specific.

Let me know if I can help more.

Ask in an Outlook Express newsgroup.
microsoft.public.outlookexpress.general is a likely candidate.