The forum only not allow giveaway thread that ask the users to making post in order to participate. But, the forum do allow if someone want to run a giveaway but asking to participate through other website/place.
He going to do it on this forum and not on another platform.
There are no prohibition to send through personal messages too, although someone that feel his PM is spam can report the PM to Admin.
unsolicited messages is a serous violation 29 rule