Is it possible to blocking Incoming emails?

  Handling Inbound Emails

Yes, there are several ways you can filter your inbound emails from being processed by Postmark.

Thre are scenarios where it’s required to block an inbound message your application doesn’t need to process it or to control your monthly utilization. A known reason for blocking an inbound message is because of malicious code, spam or abuse targeted at your inbound address and this such emails need to be blocked on the basis of spam score

In Aritic Mail, you have to option to define your own SPAM score threshold for Incoming and Outgoing emails.