SPAM (Problem and Solution)

This 

https://mxtoolbox.com/blacklists.aspx

https://multirbl.valli.org/

https://dnschecker.org/

This  https://check.spamhaus.org/ help us in looking the web that suspect in spamming. The other 

- https://mailspike.io/ip_verify

- https://www.spamrats.com/rats-noptr.php