http://marc.merlins.org/linux/exim/

Exim 4: Better and extended error messages, and postmaster callback

I rewrote my exim 3 patch to exim 4 which actually returned worse error
messages than exim 3 on header check failures. While I use it, it hasn't
gotten a lot of testing, but it seems to work fine.

To see a sample of what you get, look a these examples:
http://marc.merlins.org/linux/exim/exim4-gooderror.demo.txt
The callout option gains a new flag: check_postmaster which will ensure
that the called host also accepts mail for postmaster.
For comparison, stock exim 4 outputs messages like these:
http://marc.merlins.org/linux/exim/stockexim4.txt

The patch (v0.9) against exim 4.04 can be found here:
http://marc.merlins.org/linux/exim/patches/exim4-gooderror-4.04.diff
and the one against exim 4.05 can be found here:
http://marc.merlins.org/linux/exim/patches/exim4-gooderror-4.05.diff

These patches have been included in exim 4.11 (in a somewhat modified form)