• Invalid HELO
• What is valid?
• Invalid HELOs
• HELO is an open Proxy or Subnet
• HELO is an IP address
• HELO contain a IP part
• HELO contain my domains, subdomains or my interface by dns lookup
• HELO not contain a full host (ex: host.domain.com)
• HELO is neither FQDN nor address literal
• HELO is my hostname
• HELO is one of my Domains
• HELO is faked interface address