Whoisology is a massive, searchable database that provides an in-depth view of domain name ownership through its cross-referenced domain name whois records. The tool's priority is on reverse whois, to assist with security, cyber crime investigation, research and other business endeavors. Our appreciation for this recommendation goes to crashdodson. Source: over 1 year ago

It looks like the domain was registered in 2006 (info from https://whoisrequest.com/history/), and went offline in 2018. A long shot, but if the person who registered the site didn't hide behind a privacy option, you might be able to dig up their email address from looking into the historical WHOIS data via a site like https://whoisology.com/, or https://www.domainiq.com/. Source: almost 2 years ago

More then just reverse lookups on emails, Whoisology https://whoisology.com/#advanced Website analytics, Traffic, location, Overview etc http://www.statscrop.com/www/inteltechniques.com Youtube Video meta Data Viewer, GPS, Keywords etc http://www.amnestyusa.org/citizenevidence/. - Source: dev.to / about 3 years ago

I used these tools in the past: https://mxtoolbox.com/ https://www.mail-tester.com/. - Source: Hacker News / about 2 months ago

Suprised to not see https://mxtoolbox.com in this list too. - Source: Hacker News / 6 months ago

MX Toolbox - https://mxtoolbox.com/ - may be a place to start digging. Source: 7 months ago

You can try https://mxtoolbox.com/. Source: 7 months ago

The url I want is https://mxtoolbox.com/ and the https://mxtoolbox.org/ one redirects to malware. Source: 7 months ago