MxToolBox - All of your MX record, DNS, blacklist and SMTP diagnostics in one integrated tool.
Whoisology - Connected database of whois records and whois history
intoDNS - IntoDNS checks the health and configuration and provides DNS report and mail servers report.
Bulk Whois API - Bulk Whois API is a provider of parsed WHOIS data in JSON with simple API, competitive pricing, top notch support, and more.
SolveDNS - SolveDNS works to check your name servers, a records, and mail servers, SOA records for errors, consistency, efficiency and speed using several DNS tests.
WhoisAPI - WhoisAPI is the premier provider of freshly parsed whois data for domain names and IP addresses...