This tool tests the IP address of the mail server to check the status of the site, against more than 100 email blacklists based on DNS, if the mail server you are using is blacklisted, some of the emails you send will not be delivered.
Email blacklists are a popular way to combat spam.
Keep your site safe by checking out Mx
The method of using blacklists scanning is very easy, enter the url address, then submit, after that the site name, ip address and database are listed or not included

100% Free Blacklist Lookup too by sm seo