• What’s My DNS? – Domain Name Registrar Lookup
  • check current IP address and DNS record information against multiple nameservers
• Whois Domain Lookup – trace the ownership and tenure of a domain
• DomainTools – https://whois.domaintools.com – another Whois tool
• Hardenize – Domain Report
• DNS Checker – DNS Lookup –  finds all DNS records of a given domain name.
• DIG – Google Admin Toolbox – query the DNS of a given server 
• Into DNS – https://intodns.com – checks the health and configuration and provides DNS report and mail servers report.
• Visual Traceroute – G Suite.Tools
• SSL Checker
• DNS Inspect – checks for common DNS and mail errors.
• MX Tool Box –  MX (email) records, DNS, blacklist and SMTP diagnostics