Exim unlike "sendmail by endmail.org" makes -f
option available by default only to selected local users. Exim Doc - Trusted Users
You can change Exim configuration to:
- make the OS user trusted (
trusted_user
) or make selected OS group trusted (trusted_groups
) [but read about other things it allows] - allow all users to use
-f
(untrusted_set_sender
)