Forward to internal addresses

Forward to internal addresses

When I attempt to set up a forward to an address at my domain (internal address), I get the error "Email forwarding could not be added. Try later." For example, if my address is me@mydomain.com, I get an error if I try to forward to anotheruser@mydomain.com.  I am able to forward to an outside domain, however.  I need two separate individuals to receive message sent to a specific address.  If forwarding is not the mechanism (as it is in Gmail), I would greatly appreciate someone letting me know how this is to be accomplished.