Thank you for the prompt replay. I have enabled SPF check on Plesk. How can I however configure the mailserver so that SPF check comes first with respect to MagicSpam, or, in other words, that SPF is negatively decisive for spam attribute? Thank you again

We are an ISP. Our problem is that besides the current best practices we need absolutely th SPF control on the sender domain, so that if a server is declared as legitimate to relay for that domain no other checks must be performed and the host granted to relay.