I’ve been doing a lot of spam research lately and trying to figure out why certain email messages were being tagged as [Spam] in the subject line and others weren’t. Now, this isn’t your typical spam, it’s legit emails and ones that shouldn’t be marked. All the obvious items were checked into and no issues were found. No pills were sold, no unsuspecting targets, but the issue remained.

My main issue was with SpamAssassin. I know that it was tagging the subject of a lot of emails with [Spam] and I wanted to know why. They only thing I could really come up with was that those that were marked had FORGED_RCVD_HELO in the header source. But what does that mean?