When the Local Delivery module decides that an E-mail address is a local address, it checks that the Account with the specified name exists. Each Domain (the Main one and each Secondary Domain) has a setting that instructs the Local Delivery module on what to do if a specified Account does not exist.
If the selected option is "Rejected", all messages sent to unknown Accounts are rejected, and the error message "unknown account" is returned to the sender.
If the selected option is "Discard", all messages sent to unknown Accounts are rerouted to the NULL address, and the Server discards them without generating any error messages.
If you select the "Reroute to" option, all messages sent to unknown Accounts will be rerouted to the specified address. That address can be a name of a registered local Account, or it can be an E-mail address of an account on another server: the unknown Account address is substituted with the specified address, and the Router restarts the address processing procedure.
The specified "rerouting" address may contain the asterisk (*) symbol. In this case the name of the unknown local account is used to substitute the asterisk symbol.
The ReRoute address: firstname.lastname@example.org a message is sent to email@example.com where mycompany.com is the domain name of your Server and there is no Account james on your Server. The message is rerouted to: firstname.lastname@example.org