As of Postfix version 2.0, the Postfix SMTP server rejects mail for unknown recipients in local domains (domains that match $mydestination or the IP addresses in $inet_interfaces or $proxy_interfaces) with "User unknown in local recipient table".
See the standard modules page for a list of all the functions built into Webmin.
This is a list of notable port numbers used by protocols of the transport layer of the Internet protocol suite for the establishment of host-to-host connectivity.
Originally, port numbers were used by the Network Control Program (NCP) in the ARPANET for which two ports were required for half-duplex transmission.
A recipient address is local when its domain matches $mydestination, $inet_interfaces or $proxy_interfaces.
If a local username or address is not listed in $local_recipient_maps, then the Postfix SMTP server will reject the address with "User unknown in local recipient table".