Set up as transparent bridge SPAM blocker
Is it possible to setup pfsense as a transparent bridge to be able to block outgoing SPAM on our network?
SPAMD or some other method? Or is this not possible in transparent mode?
Block outbound SMTP 25 from any device except authorized SMTP servers. This will solve a multitude of issues.
In addition to SubMicron's excellent answer, I'd add that you should enable logging of blocked SMTP senders so that you can find the rogue PC(s).
Then go to their desks.
And shoot them.
Well, I'm afraid this is not an option as the network contains web servers with "unknown" SMTP senders, so we would not know who to block and not to block. This is why we are looking at the "SPAMBLOCKER" route for outgoing traffic.