I suppose that is one reason why some sites use separate MTAs for
their inbound and outbound mail. The inbound MTA strips SRS from
local recipients, and the outbound MTA adds SRS to local senders
Why do I want to add SRS to local senders?
I need SRS for non-local senders, primariliy to forward local addresses
to external domains.
This model can be implemented with Postfix using the existing
content-manipulation interfaces.
Ok, adding SRS can be done by a filter plugin (getting the alias domain
out of the original recipient is not necessarily a must-have feature),
but then the filter needs to know which domains are local.
I looked at the patch, and the approach taken there is limited to
MTAs that perform final delivery (the decision to un-SRS the recipient
is hard-coded for final delivery only). That is a major limitation.
This does not work on a mail gateway configuration, where Postfix
is a transit MTA that handles mail on behalf of one or more internal
MTAs. Transit MTAs don't perform final delivery - that is done by
the internal MTAs (Postfix-in-front-of-Exchange being one example).
For incoming mail I don't see the problem to un-SRS the recipient if we
have the appropriate secret. In smtpd there's only a check if the
SRS-address is valid, rewriting itself is done in cleanup together with
canonical address mapping.
I doubt to use SMTP-milter since it can't make modifications to the
envelope. Or does this limitation only apply if additionally using a
content filter?
