Enter a URL
A blacklist / blocked list check will show if the URL or IP address entered is in the DNSBL or SURBL systems. Email system administrators use these systems to try to get rid of spam emails before they reach their users.
DNSBL is a domain name blacklist/block list. There are dozens of DNSBLs online, all of which use a variety of criteria for listing and removing addresses. Spam filters use various DNSBLs to verify that incoming emails do not originate from blacklisted sites. DNSBLs are generally the first line of defense against spam.
Why is my IP blacklisted?
SURBLs (which are no longer an acronym) are generally the second line of defense, but not all spam filters can use them. SURBLs are blacklists of websites that have been observed to appear in spam emails. The spam filters that SURBL can use scan the body of email messages, extract website addresses, and compare them to blacklists. If an address is found, the message will be marked as spam and treated accordingly.
Since both methods are filtered differently, they are most effective when combined. Unfortunately, as spammers get smarter, there is no way that all spam can be detected. It is interesting to note, given the methods spammers use, that DNSBLs tend to change more frequently than SURBLs. If you are an email system administrator and your server is blacklisted, you will have to work with different DNSBLs that may be on the list and/or SURBL (https://seofreetools.org/).