To enable a local server relay mail through exchange server we need to add the local server to the Exchange server allowed relay servers list.
To add a server to the Relay list:
Open Exchange system Manger – > Administrative tools –> First administrative group -> Server -> Click on the Exchange server -> Protocols -> SMTP -> Right Click on Default SMTP Virtual Server -> Properties -> click on Access Tab – > click on Relay button -> Add the server to the “only the list below” list.