How to Use MxToolbox's MX Lookup Tool

Updated

Go to mxtoolbox.com's MX Lookup page, enter the domain you want to check, and submit it. The tool returns that domain's MX records in priority order. Because the lookup runs directly against the domain's authoritative name server, recent MX record changes should appear immediately rather than waiting on cached results. From the results you can also run Diagnostics on a mail server, which connects to it, verifies reverse DNS records, performs a simple Open Relay check, and measures response time.

What the MX Lookup tool does

MX records tell the internet which mail servers accept email for a domain, and in what order they should be tried. MxToolbox's MX Lookup lists those records for a domain in priority order.

The page's own description notes one detail that matters when you are troubleshooting: the lookup is done directly against the domain's authoritative name server, so changes to MX records should show up instantly. That makes it useful right after you edit DNS and want to confirm the change is live.

Step-by-step: running a lookup

  1. Open the MX Lookup tool on mxtoolbox.com.
  2. Enter the domain name you want to check (for example, the domain whose email delivery you are diagnosing).
  3. Submit the lookup.
  4. Read the results: MX records are listed in priority order, so you can see which mail server is preferred and which are fallbacks.

Note that the site requires JavaScript — the page states JavaScript is required for the site, so a browser with JavaScript disabled will not run the tool.

Going further with Diagnostics

Once you have the MX records, you can click Diagnostics. According to the tool's description, Diagnostics will:

  • Connect to the mail server
  • Verify reverse DNS records
  • Perform a simple Open Relay check
  • Measure response time performance

You can also check each MX record (its IP address) against 105 DNS-based blacklists, commonly called RBLs or DNSBLs.

What you can conclude from the results

What you see What it suggests
MX records listed in priority order The domain has mail routing configured; lower priority numbers are tried first
A recent change not appearing Unlikely to be a caching delay, since the lookup goes straight to the authoritative name server
Diagnostics connection or reverse DNS problems The mail server may have reachability or PTR record issues worth investigating
An MX IP listed on blacklists The sending reputation of that server may be affecting deliverability

Practical notes

  • The tool reports your own IP on the page, which is handy context when you are checking whether your sending server is the one being tested.
  • Blacklist checks are per MX record IP, so a domain with several mail servers may show different results for each.
  • The page lists contact and legal links (Terms & Conditions, Security, API, Privacy) plus a phone number, so there is an API path if you want to automate lookups rather than use the web form.