Dear All, I have a exchange server 2003 which is having nearly 350 users. One strange thing I observed that in outlook express if I put my server ip in incoming and outgoing server and define any name than that id can send a mail to internal as well as to the external users such as gmail and rediffmail. No need to create any type of id in exchange you can take any name and configure in outlook express u will be able to send a mail to anyone with display name like username@companyname.com . But if u replies to same id you will get NDR. Can anyone let me know why this is happening?