PostSRSd ======== About ----- PostSRSd provides the Sender Rewriting Scheme (SRS) via TCP-based lookup tables for Postfix. SRS is needed if your mail server acts as forwarder. Sender Rewriting Scheme Crash Course ------------------------------------ Imagine your server receives a mail from `alice@example.com` that is to be forwarded. If example.com uses the Sender Policy Framework to indicate that all legit mails originate from their server, your forwarded mail might be bounced, because you have no permission to send on behalf of example.com. The solution is that you map the address to your own domain, e.g. `SRS0+xxxx=yy=example.com=alice@yourdomain.org` (forward SRS). If the mail is bounced later and a notification arrives, you can extract the original address from the rewritten one (reverse SRS) and return the notification to the sender. You might notice that the reverse SRS can be abused to turn your server into an open relay. For this reason, `xxxx` and `yy` are a cryptographic signature and a time stamp. If the signature does not match, the address is forged and the mail can be discarded. Building -------- PostSRSd requires a POSIX compatible system and CMake to build. Optionally, help2man is used to create a manual page. For convenience, a Makefile fragment is provided which calls CMake with the recommended command line options. Just run `make`. Alternatively, you can control many aspects of the build manually: mkdir build cd build cmake .. make make install The CMake script defines a number of options in addition to the standard CMake flags. Use `-D