Integration Method 2

Since version 4.00, exim includes an interface designed specifically to integratn an external program to make policy decisions. This interface is called ``local_scan''. Marc Merlin maintains sa-exim, an implementation of the local_scan API which uses Spamassassin as the decision mechanism.

sa-exim has many advantages over the technique detailed in Integration Method 1 above :

• each message is handled by exim only once
• there is less overhead to scanning (because each message is handled only once)
• tracking a message in the logs is easier (because each message is handled only once)
• statistical reporting (eg by eximstats) won't be grossly skewed (because each message is handled only once)
• spam messages can be rejected during the SMTP session -- this maintains the reliability built in to the SMTP protocol while at the same time relieving your system of the burden of undeliverable bounces or delivering the spam to the user

For more details on sa-exim, installation instructions and source code see Marc's site: http://marc.merlins.org/linux/exim/sa.html.

(A note for Debian users: the (recent) exim4 package includes the ``dlopen'' patch Marc also maintains. The dlopen patch is a local_scan implementation that uses the dlopen(3) system call to dynamically load a separately compiled local_scan function from a .so. This eliminates the need to recompile exim when you want to change/upgrade the local_scan implementation.)

I recommend using sa-exim instead of the methods described earlier in this document.