Rule set 1 is intended to process all sender addresses. It is rarely used but can find application at sites where all outgoing mail should appear to come from a central mail server. Rules to handle this host hiding might look like this:
R$- $@ $1 <@ $R> user => user@ourdomain R$* <@ $=w> $* $@ $1 <@ $R> $3 user@localhost => user@ourdomain
In the LHS the
$=w matches any name from a list of names by
which the local host is known. In the RHS the
contains the name of the mail server. If the mail is not from
the local host, it is unchanged.
Other uses for rule set 1 might include the following:
Normalizing senders, for example, making mail from the users operator and dumper appear to come from root.
Hiding user login names by mapping them (through an external database) to the form firstname.lastname.
Needless to say, great care should be exercised in adding schemes such as these to your configuration file.