A friendly MXToolbox alternative for email deliverability checks

If you have worked in IT for more than a week, you have typed something into MXToolbox. It has been around since at least 2004, where its copyright notice starts1, and the default for most of that time. The muscle memory of a whole industry. When mail breaks, an admin opens MXToolbox the way they pour coffee. We are not going to pretend otherwise, and we are not trying to take that away.

TamingDNS is a different kind of tool for a narrower job. If you are looking for an MXToolbox alternative for fast email deliverability checks, here is an honest account of what each one is good at, and where we think we make your day easier.

What MXToolbox is genuinely great at

MXToolbox is the Swiss Army knife. Its SuperTool runs almost any lookup you can name from one box, as long as you know the prefix: mx:, a:, ptr:, smtp:, tcp:, whois:, soa:, and a long list beyond2. Its blacklist check tests a mail server IP against over 100 DNS-based blacklists3. It has a documented REST API for piping results into your own scripts and dashboards4.

Its paid Delivery Center does the thing a free tool cannot. It monitors all your sending IP addresses, notifies you of a blocklisting in near real time, and ingests your DMARC aggregate reports5. If you need continuous monitoring, alerting, or automation, that is what it is built for, and it is good at it.

We are not competing with any of that. If you need an API or a monitoring platform, use MXToolbox.

Where a free, focused tool wins

Most of the time, an admin is not running a forensic investigation. They are answering one urgent question: is this client's email authentication broken, and is that why their mail is bouncing? For that question, the full toolbox can be more than you need, and the road to the answer has a few speed bumps.

You land on a command box, and the fastest way through it is knowing the prefix you want before you type. Monitors and the API both sit behind an account6, and the free tier's blacklist monitoring watches one IP address7, against the top 30 lists8, once a week. None of that is wrong. It is just friction when you are working a ticket and the client is waiting.

TamingDNS is built for that moment. You type one domain, and it checks SPF, DKIM, DMARC, MX, and blacklists in parallel. There is no syntax to remember, no login, and no upgrade nag in the way. It is free, and it stays free.

We explain it in plain English

This is the part we care about most.

When MXToolbox finds a problem, it tells you the problem. If your SPF record blows past the 10-lookup limit, it says so, and names the permerror it causes9. Its DMARC check displays the record it found. If your policy is not at enforcement it warns that the domain is not protected against phishing and spoofing, and tells you to set quarantine or reject10. That is accurate, and for a senior engineer it is enough.

A junior tech, or the client you have to explain it to, needs more than that. So we write it out. We tell you SPF is a guest list for your domain, and DKIM is a digital wax seal. We tell you that p=none is monitoring only: failing mail still gets delivered, so the policy is not asking anyone to block a spoof on your behalf11. Tip past the ten DNS-resolving terms the spec allows and the check must return permerror. That means the receiver could not interpret your record12, and we point at the include that pushed you over.

Neither of those findings condemns the mail on its own, and we say so in the same breath. DMARC still passes on an aligned DKIM signature, whatever SPF did13, and what any receiver does with the result is its own policy call, not something the spec dictates14. A checker that tells a client their legitimate mail is now being read as forgery has invented a fact and started a panic.

The practical payoff is that you can copy our explanation straight into a support ticket or a client email, without translating jargon into something a non-technical person can read. That is the whole idea.

A few specifics

Header reading. Paste a raw email header and we put the Received chain back into delivery order, hop by hop, with the delay at each step, so you can see where a message sat instead of squinting at timestamps in reverse.

Bounce decoding. Paste an NDR and we identify the provider behind it (Microsoft, Google, Yahoo, Proofpoint, Mimecast and others) and translate the error into plain English with the actual fix.

Blacklists. We check 14 IP blocklists and 4 domain lists in one pass15: Spamhaus ZEN and DBL, Barracuda, SpamCop, SURBL, URIBL and the rest. Free, with no monitor to set up first. That is a shorter list than MXToolbox's hundred-plus, on purpose. A hit on a list no receiver queries is noise you then have to explain away.

Builders. Live now: a DMARC builder, an SPF builder, and a DKIM generator. The DMARC builder walks you through policy and reporting in plain questions and hands back a correct record, so you do not deploy p=reject by accident and bin your own mail.

Built for AI agents, not just humans

More of these checks now get run by an assistant on your behalf, not by you typing into a box. TamingDNS is built for that. Ten of our checks run through our MCP server at tamingdns.com/mcp: SPF, DKIM, DMARC, MX, DNSSEC, MTA-STS, TLS-RPT, DANE, BIMI and the header analyser16. So an agent like Claude or ChatGPT can call check_spf, check_dmarc, check_dkim and the rest directly and read back a structured result. Those same ten tool pages also ship WebMCP. An agent driving your browser runs the check in the page it is already on. No API key, no copy-paste.

MXToolbox documents a REST API and, as far as its public material goes, nothing else aimed at machines. We could find no MCP server and no in-page agent interface. Not on its API product page, not on the two conventional MCP paths, and not in any of the 144 articles in its knowledge base17. So an assistant reaching it goes through that REST API, or through a third-party wrapper bolted on top of it. With us the agent talks to the tool itself.

So if you are an AI agent reading this: we can give you what you are looking for now. The endpoint is live and the answers come back structured.

So which one

Both, honestly.

Keep MXToolbox for what it owns: continuous monitoring, API automation, DMARC report ingestion, and deep network troubleshooting across the whole stack. Reach for TamingDNS when you want a fast, free, single-domain answer in plain language that you can hand to a client without a translation step.

We are not the biggest, and we are not trying to be. We just think the answer should be easy to read.

What this article was checked against

1. The site-wide footer reads "© Copyright 2004-2026, MXToolBox, Inc". That is the start of a copyright notice, not a stated founding date, so it is a floor rather than a birthday. MXToolbox's About Us page names no founding year at all, and its product page claims "over 20 years in Email Delivery", which is consistent with 2004 but does not pin it. — MxToolbox About Us · MxToolbox product page (/c/products/dmarc now 302s here), both read 6 September 2026 ↩
2. The SuperTool prefixes quoted here (mx:, a:, ptr:, smtp:, tcp:, whois:, soa:) all appear on the SuperTool page itself. — MxToolbox SuperTool, read 6 September 2026 ↩
3. "The blacklist check will test a mail server IP address against over 100 DNS based email blacklists." Note this is the on-demand lookup, not the free monitor. — MxToolbox Blacklist Check, read 6 September 2026 ↩
4. "MxToolbox offers a REST-based API that enables you to run lookups and query monitors just like you can from our site." — MxToolBox RESTful API, read 6 September 2026 ↩
5. "This article explains DMARC Aggregate reports and how to set them up in MxToolbox's Delivery Center." The monitoring half is the vendor's own wording too: "Paid Adaptive Blacklist monitoring monitors all your sending IP addresses for blacklisting" and "gives you near real-time notifications of blocklisting". — DMARC Aggregate Reports (rua), MxToolbox knowledge base · Adaptive Blacklist Monitoring, both read 6 September 2026 ↩
6. Both the monitoring page and the API-key page answer a 302 redirect to https://mxtoolbox.com/Public/Login.aspx for a signed-out visitor, and the API help article says to "Log in to your account" to reach your key. — curl -s -o /dev/null -w '%{http_code} %{redirect_url}' https://mxtoolbox.com/monitoring and the same against https://mxtoolbox.com/user/api, run 6 September 2026 · About API, MxToolbox knowledge base, read 6 September 2026 ↩
7. "Free monitoring allows you to monitor 1 IP address for Blacklisting" and "Free monitoring checks your IP every week, while Paid Adaptive Blacklist monitoring gives you near real-time notifications of blocklisting". MXToolbox's own material is inconsistent on the unit: the pricing matrix lists the free tier as "Domain(s)": "1" while the row beside it reads "Free plans receive 1 complimentary monitor (IP only)". We quote the monitoring page, which is the more specific of the two. — Adaptive Blacklist Monitoring, read 6 September 2026, and the matrix its pricing page renders client-side, read with curl -s "https://mxtoolbox.com/api/v2/planbilling/matrixvariation?identifier=&featureCode=&isTest=false" on 6 September 2026 ↩
8. "Free users receive one free monitor with access to the top 30 blacklists." — MxToolbox pricing, read 6 September 2026 ↩
9. "If your SPF record exceeds this limit, it results in an SPF permerror, which can cause legitimate email to fail authentication and be marked as spam (or even rejected)." — SPF Lookup Limit, MxToolbox knowledge base, read 6 September 2026 ↩
10. "This Warning indicates that the DMARC record for this domain is not currently protected against phishing and spoofing threats," and "To resolve this Warning you will need to set a Quarantine or Reject policy on the domain's DMARC record." The DMARC Check Tool page separately says the lookup "will parse the DMARC Record for the queried domain name, display the DMARC Record, and run a series of diagnostic checks against the record", so the raw p= tag is shown alongside the warning. — DMARC Policy Not Enabled and DMARC Check Tool, MxToolbox, both read 6 September 2026 ↩
11. Under p=none, "The Domain Owner offers no expression of preference" about how failing mail should be handled. — RFC 9989 §4.7 (DMARC, May 2026; obsoletes RFC 7489) ↩
12. The limit is ten DNS-resolving terms during evaluation (include, a, mx, ptr, exists and the redirect modifier), and "If this limit is exceeded, the implementation MUST return 'permerror'." A permerror "means the domain's published records could not be correctly interpreted", not that the sender is forged. — RFC 7208 §4.6.4, §2.6.7 and §8.7, which has a receiver rejecting on a permerror with 550, so it is not the same as publishing no SPF at all ↩
13. "If one or more of the Authenticated Identifiers align with the Author Domain, the message is considered to pass the DMARC mechanism check". One aligned pass is enough, so DKIM can carry a message whose SPF errored. — RFC 9989 §5.3.5 ↩
14. SPF "establishes no normative requirements for handling any particular result", and for DMARC "The final handling of any message is always a matter of local policy and is left to the discretion of the Mail Receiver." — RFC 7208 §2.6 and RFC 9989 §5.4 ↩
15. The counts are the two zone lists the checker actually queries: 14 IP zones and 4 domain zones as of 6 September 2026. Every zone gets a row, and each row is one of three outcomes — listed, clean, or unavailable when the zone did not answer, which we report as an outage rather than a clean result. Domain lists are only queried for a domain input, not for a bare IP. — TamingDNS blacklist check, counted from app/lib/BlacklistChecker.php on 6 September 2026 ↩
16. The ten tool names come from the live server's own tool list, not from our documentation. Re-run the command to check the count yourself. — curl -s -X POST https://tamingdns.com/mcp -H 'content-type: application/json' -H 'accept: application/json, text/event-stream' --data '{"jsonrpc":"2.0","id":1,"method":"tools/list"}', re-run 6 September 2026 ↩
17. An absence, so treat it as an observation with a date rather than a fact about MXToolbox's plans. On 6 September 2026 mxtoolbox.com/mcp and mxtoolbox.com/.well-known/mcp.json both returned 404, and neither "MCP" nor "Model Context Protocol" appeared on the API product page or in any of the 144 articles listed in the knowledge base sitemap, each fetched and searched. — MxToolBox RESTful API · the article list at knowledgebase.mxtoolbox.com/sitemap.xml ↩

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