Everyone know common dns blacklists used for rejecting emails. To check, if ip address is blacklisted on some blacklist, it is common to use service like mxtoobox.com. But what check next, if mxtoolbox shows ip is not blacklisted and email or connections are still rejected (sometimes without any reason) by some servers?
Many commercial devices uses own commercial blacklists. So fare, I have know about
SenderBase Security Network used by Cisco IronPort
Symantec IP Reputation Investigation used by Symantec products (Brightmail)
Commtouch ip reputation used by Commtouch antispam (ctasd)
Fortinet FortiIP used by Fortigate products (FortiGuard)
Junk Email Filter free hostkarma.junkemailfilter.com blacklist