What Is MxToolbox?

Updated

MxToolbox is a free online network diagnostics platform best known for its MX Lookup tool, which lists a domain's mail exchanger (MX) records in priority order. It's aimed at IT staff, email administrators, and domain owners who need to troubleshoot email delivery problems or verify DNS configuration. The MX lookup queries the domain's authoritative name server directly, so record changes should appear immediately rather than waiting on cached results.

What the MX Lookup tool does

The core function is straightforward: you enter a domain name, and the tool returns its MX records sorted by priority. Because the query goes straight to the authoritative name server, you see the current state of the zone rather than a stale resolver cache.

From there, the tool offers additional checks:

  • Diagnostics — connects to the mail server, verifies reverse DNS records, runs a simple Open Relay check, and measures response time performance.
  • Blacklist checks — each MX record (by IP address) can be checked against 105 DNS-based blacklists, commonly called RBLs or DNSBLs.

These checks matter because MX records alone don't tell you whether mail will actually be delivered. A correctly configured MX record pointing at an IP that appears on a blacklist, or one with a broken reverse DNS entry, can still cause delivery failures.

Who it's for

The tool fits a few common situations:

  • Email administrators diagnosing why messages to or from a domain are bouncing or being rejected.
  • IT staff verifying that DNS changes propagated as expected after a migration or provider switch.
  • Domain owners checking whether their mail setup is configured correctly, especially after changing hosting or email providers.

Practical notes

The site requires JavaScript to function, so a browser with JavaScript enabled is necessary. The MX lookup itself needs no account or login based on the available information. Beyond the lookup, the diagnostics and blacklist checks are the features most likely to surface the actual cause of a delivery problem — a working MX record is only the first step.

For a quick answer to "is this domain's mail routing set up correctly?", the MX Lookup is the starting point. For "why is mail from this domain being blocked?", the diagnostics and blacklist checks are where the useful detail lives.