Normally, header recipient addresses
and header and envelope sender addresses that are local are left as
is. If the always_add_domain feature is defined,
local addresses that lack a host part have an @
and the MASQUERADE_AS host appended (if it is defined). If
MASQUERADE_AS is not defined, an @ and the value
of $j sendmail macro ($j) are appended.
The form for the always_add_domain feature is:
The always_add_domain feature is safe and
recommended. It ensures that all addresses that are locally delivered
will be fully qualified. See the allmasquerade
feature (FEATURE(allmasquerade)) for a description of the risks
surrounding masquerading addresses.