Prior to V8.7 sendmail,
only the local delivery agent could cause the
localaddr rule set 5 to be called (Section 19.6). The localaddr rule set 5
is called after aliasing and before forwarding, and can be used to
select a new delivery agent. Beginning with V8.7, any delivery agent
with the F=A delivery agent flag set (F=A) can cause an address to be looked up in the
aliases(5) file. Therefore, any delivery agent
that has the F=A and F=5
delivery agent flag set will cause the localaddr
rule set 5 to be called as though the agent were the
local delivery agent.
In configuration files prior to Version 6 (Section 17.5), this delivery agent flag is automatically
set for the local delivery agent. Note that
addresses that (perhaps artificially) begin with an
@ character cause the localaddr
rule set 5 to be skipped (Section 19.6).