When an IP address from the email header's "Received" field and the domain in the email address are identified, their authenticity can be analysed using websites that maintain updated lists of blocked IP addresses and domains:

• MultiRBL – provides information about the internet service provider associated with the IP addresses.
• Autonomous System Lookup – offers information about the internet service provider associated with the IP addresses.
• Spamhaus – combines and contains one of the most comprehensive lists of blocked IP addresses.