Prior to V8.7
sendmail, only the local
delivery agent could recognize the :include:
directive for creating mailing lists (Section 13.2).
Beginning with V8.7, any delivery agent can be made to recognize the
:include: directive by setting the
F=: delivery agent flag (or to ignore it by not
setting the F=: delivery agent flag). This
delivery agent flag allows you to design a local
delivery agent without :include: support or
local-type clones with :include: support. In
configuration files prior to Version 6 (Section 17.5), this delivery agent flag is automatically
set for the local delivery agent.
This delivery agent flag is legal only for addresses contained in
~/.forward files or
aliases(5) databases. Any
:include: address in an SMTP dialog or on the
command line will be rejected.