qmail-sppprovides plug-in support for qmail-smtpd. It allows you to write external programs and use them to check
SMTPcommand argument validity. The plug-in can trigger several actions, like denying a command with an error message, logging data, adding a header and much more.
- Author: Pawel Foremski
- More info here
Today I played for the first time with an ancient patch for
qmail-spp and I was really impressed for the ease of use and the elegance of its code, which is inserted inside
qmail-smtpd.c with a few touches, despite of the many things that it can do when installed and enabled.
It can run a custom plugin in any language and at any level of the
smtp session, grabbing the environment variables, writing into
stderr or blocking the
smtp session with a return error for the sender.
Of course I decided to add this patch to my combo. I've just modified the way it has to be enabled, just not to bother those who don't want to touch their run scripts. So, while the original patch is enabled by default, I modified things a little bit so that you have to manually enable it by exporting the variable
ENABLE_SPP in your run scripts. Therefore the original
NOSPP variable is useless.