I understood why Exim doesn't provide that. But a lot of people still want the
future and wide range of different configurations of exim is used all around
the world so ... people can and may use it for their own risk.
My vision is:
- add one extra option in Makefile (FUTURE_DSN) that is commented by default.
- if the future is on, you will have two new variables (for ex.
dsn_request=0|1 and dsn_requester_address) which can be used in
shadow transport, conditions, filters and so on
- exim will not generate any delivery report itself.
After that exim can be used as DNS-aware mailer and everyone can construct its
own configuration with DSN-support
