intoDNS - IntoDNS checks the health and configuration and provides DNS report and mail servers report.

MxToolBox - All of your MX record, DNS, blacklist and SMTP diagnostics in one integrated tool.

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.

DNSInspect - DNS is a free online service to check your domain’s servers for common DNS and mail errors and produces a report with explanations how to fix them.

Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.

DNS Checker Tool - Check Domain Name System (DNS) records for any website.