F=C delivery agent flag causes
sendmail to append an
@domain extension to any recipient address that
lacks one after having been rewritten by the
canonify rule set 3. The
@domain that is added is copied from the
envelope sender's address.
This F=C delivery agent flag is not looked for in
the delivery agent definition that was selected to send the message.
Rather, it is looked for in the delivery agent that would be selected
if the sender were the recipient (as in the case of bounced mail).
To illustrate, consider the following mail:
To: firstname.lastname@example.org, alice
The recipient address alice lacks an
@domain specification. The
sendmail program processes the envelope sender
address email@example.com to decide on a delivery
agent definition that can be used if this mail needs to be returned.
If that envelope sender's return mail delivery agent
has the F=C delivery agent flag set, the
@oursite.edu part of the envelope
sender's address is appended to
To: firstname.lastname@example.org, email@example.com
The F=C delivery agent flag is traditionally used
for the smtp class of delivery agent that is
supposed to always supply an @domain part for
Note that the domain part of the envelope sender
is used. In our example the envelope and header sender are the same.
See also the always_add_domain feature (FEATURE(always_add_domain)).