intoDNS - IntoDNS checks the health and configuration and provides DNS report and mail servers report.
Whoisology - Connected database of whois records and whois history
MxToolBox - All of your MX record, DNS, blacklist and SMTP diagnostics in one integrated tool.
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.
NsLookup.io - A simple and powerful tool for querying DNS records
WhoisThisDomain - Domain name lookup tool that allows you to get information about domain registration from WHOIS server.