The “Contact Us” form in vBulletin is highly susceptible to spamming. I’ve received 100% spam from it– no legitimate emails. 32 spam emails so far.. the forum is inactive anyway, so I’m shutting it down.
Update (8/20/2007): Did a Google search for vBulletin Spam and this post came up 4th. Unfortunately, I still get lots of spam on my vBulletin forum. This is very hard to combat.
vBulletin options > Site Name / URL / Contact Details > Allow Unregistered Users to use ‘Contact Us’ = Yes, but Verify Image
