MxToolBox - All of your MX record, DNS, blacklist and SMTP diagnostics in one integrated tool.
SPF Toolbox - SPFtoolbox is a Javascript and PHP app to look up DNS records such as SPF, MX, Whois, and more
intoDNS - IntoDNS checks the health and configuration and provides DNS report and mail servers report.
BlacklistAlert - BlacklistAlert is a simple to use website that offers the lookup service to its client.
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.