MxToolbox blacklist check: what the free tier covers and where it stops

MxToolbox is a free-to-start diagnostic platform that checks your domain or IP against 100+ DNS-based blacklists in a single scan. It also runs MX record lookups, SMTP diagnostics, and SPF/DKIM/DMARC validation. The free tier covers unlimited manual lookups. Paid plans (from $19/month) add automated monitoring and alerts.

The blacklist check is the feature most people come for — and honestly, it works well enough that a lot of IT admins never bother looking at anything else. This post focuses on what the free tier actually does, what it misses, and when paying makes sense.

Pros and cons

How the MxToolbox blacklist check works

Go to mxtoolbox.com/blacklists.aspx or type blacklist: followed by your IP or domain in the SuperTool.

MxToolbox queries 100+ DNS-based blacklists (RBLs) at once and returns color-coded results within seconds. Green = not listed. Red = actively listed on that blacklist. Each red result links directly to the blacklist provider’s delisting page, which saves you the headache of hunting down the right form.

The scan checks your sending IP or domain against major RBLs including Spamhaus, Barracuda, SORBS, and SpamCop. Even a single listing on a major RBL like Spamhaus can tank your deliverability across Gmail, Outlook, and Yahoo overnight.

What to do if you are blacklisted

1. Fix the root cause first. Compromised accounts, open relays, purchased email lists, and shared hosting IP reputation are the usual culprits. If you skip this step, you will end up back on the same blacklist within days.
2. Submit a delisting request with each blacklist provider that flagged you. Most process requests within 24–72 hours, though Spamhaus can be slower if your IP has repeat offenses.
3. Re-run the MxToolbox check after 48 hours to confirm the listing has cleared.

What else the free tier includes

The blacklist check gets the most use, but MxToolbox is really a full suite of DNS and email diagnostics. Everything below is free and unlimited.

MX lookup

Pulls all MX records for a domain with priority values and resolved IPs. This is usually the first thing to check when email routing breaks.

DNS lookup

Fetches any DNS record type — A, AAAA, CNAME, MX, TXT, NS, PTR, SOA — from live servers, not cached data.

SPF, DKIM, and DMARC checks

The SPF check counts your DNS lookup chain and flags if you exceed the 10-lookup limit (which causes a PermError at receiving servers). The DKIM check verifies your public key is published and correctly formatted. The DMARC check reads your policy record and flags gaps — like a policy of none with no reporting addresses, which means you are collecting zero data on who is spoofing your domain.

SMTP diagnostics

Connects to your mail server, simulates the SMTP handshake, checks the banner, response codes, and TLS availability. Useful for catching misconfigured servers that silently reject or defer mail without any visible error on your end.

Domain health report

Runs 30+ tests at once — DNS, blacklists, SMTP, SPF, DKIM, DMARC — and returns a scored, color-coded report. Good for a quick triage when you are not sure where to start.

SuperTool

One search bar for everything. Prefix your query with mx:, blacklist:, smtp:, or spf: to run that specific check without navigating to separate pages. Once you get used to it, you will probably never use the individual check pages again.

Free vs. paid: full comparison

Pricing is approximate as of 2026. Check mxtoolbox.com for current rates.

The free tier handles one-off diagnostic checks and DNS verification. Paid plans make sense when you need to know about blacklisting events as they happen rather than finding out after your open rates have already cratered.

MxToolbox vs. alternatives

MxToolbox wins on breadth — no other free tier gives you blacklist checks, DNS lookups, SMTP diagnostics, and authentication validation all in one place. For dedicated DMARC reporting with aggregate and forensic views, dmarcian goes deeper. For inbox placement testing (will this specific email land in Primary, Promotions, or Spam?), GlockApps is more targeted.

Delivery Center: what paid monitoring adds

The Delivery Center is MxToolbox’s continuous monitoring dashboard for paid subscribers. It watches your infrastructure around the clock and alerts you when a blacklisting event occurs, a DNS record changes, an SMTP server goes offline, or an authentication record is modified.

Blacklist checks run multiple times per day instead of on-demand, so new listings are typically caught within hours rather than days. For teams managing email at scale, the API lets you pipe results into existing monitoring stacks and ticketing systems — handy if you already run everything through PagerDuty or Datadog.

Frequently asked questions