https://mxtoolbox.com
https://www.mail-tester.com
https://www.dnswatch.info
https://intodns.com
https://check.spamhaus.org
https://www.learndmarc.com
https://bezpiecznapoczta.cert.pl
https://postmaster.google.com
https://multirbl.valli.org
https://sender.office.com
https://sendersupport.olc.protection.outlook.com/snds/index
https://iplocation.io/