We check emails for:

• Spamcop
• Spamhaus spam & exploxit blocking lists
• DNS realtime blacklist
• Not just another bogus list
• Spam and open relay blocking system
• Composite blocking list
• Distributed sender blackhole list
• Live dynamic distributed blacklist
• Reverse DNS entries
• Country or origin
• Previous spam attempts

• Valid sender MX records
• Valid sender SPF records   
• Valid recipient addresses
• Keywords likely to be found in spam
• Embedded images which are likely to be found in spam
• URL's listed in spam URI realtime blocklist
• Bayesian statistical spam probability test
• Viruses or password protected archives