In modern usage, the local or "l" channel's main use is as a placeholder in identifying "local" addresses, in that (normally) only addresses that initially rewrite to the local channel will be checked for MTA aliasing. (See, however, the
aliaslocal channel option.) The presence of the
viaaliasrequired channel option on the "l" channel is critical both operationally and for security purposes, as it enforces that only those addresses that have a successful alias lookup (hence correspond to a provisioned address) are accepted as valid "local" addresses.
In principle, the local channel could also be used to deliver messages to UNIX mailboxes on the local host; however, that use is deprecated.
In principle, the local channel would also be considered to be the source of messages submitted on the iMS host itself via utilities such as
imsimta send, etc.; however, such submission is mostly moot nowadays.
Configuration settings on the "l" channel are somewhat privileged, since it is taken (in the absence of overriding configuration settings) as the default set of names for the MTA system itself. See the
notices channel option. And compared to the "l" channel
official_host_name, see the
received_domain MTA options and the BANNER_HOST TCP/IP-channel-specific option for some examples of configuration options to override this "l" channel value.