After all Routing Table records are applied, the Router checks if the domain name is the external string. In this case, the domain part is cut off, and the local part is passed to the External Authenticator program.
The external program can use any method to process the supplied address, and it should return a modified address or an error code.
If a modified address is returned, the Router makes the next iteration with this new address.
Signals to addresses starting with 011 in any local Domain should be routed using an external Helper program. You can implement this routing using the following record: NoRelay:Signal:<011*@> = tele-@external ; route using an external program
If a Signal is sent to email@example.com, where local.domain.dom is a local Domain, the address will be rerouted to tele-5556666@external and the External Helper will receive a request to route the tele-5556666 address.