MX ToolboxMX Toolbox is an Austin, Texas company that provides free and reliable network diagnostic and lookup “super tools” used by a global tech community to troubleshoot infrastructure issues. For years I’ve used MX Toolbox whenever I’m having trouble with a client’s mail or DNS servers. It is one of those tools I take for granted which is why it has taken me a while to post it as one of the Cool Tools.

MX Lookup - This test will list MX records for a domain in priority order. The MX lookup is done directly against the domain’s authoritative name server, so changes to MX Records should show up instantly.

Blacklist - This test will check a mail server IP address against over 100 DNS based email blacklists (commonly called Realtime blacklist, DNSBL, or RBL).  If your mail server has been blacklisted, some email you send may not be delivered.  Email blacklists are a common way of reducing spam.

SMTP Diagnostics – his test will connect to a mail server via SMTP, perform a simple Open Relay Test and verify the server has a reverse DNS (PTR) record.  It will also measure the response times for the mail server.

MX Subnet Calculator – The subnet calculator lets you enter a subnet range (CIDR) and see IP address information about that range. It also lists each IP address in the range and automatically does a Reverse IP Lookup.

Email Header Analyzer - This tool will make email headers human readable by parsing them according to RFC 822.  Email headers are present on every email you receive via the Internet and can provide valuable diagnostic information like hop delays, anti-spam results and more.

DNS Lookup - This test will list DNS records for a domain in priority order. The DNS lookup is done directly against the domain’s authoritative name server, so changes to DNS Records should show up instantly.

These are just some of the tools available. You can access the complete suite of tools here, including ping and traceroute. Of course, MX Toolbox offers a host of professional services such as MXWatch Monitoring and MailFlow Monitoring.