Merlonix vs MXToolbox: Deep Lookups vs. Continuous Monitoring
MXToolbox is one of the most-used diagnostic tools on the internet. Its SuperTool runs DNS, MX, blacklist, SPF, DMARC, and DKIM lookups from a single box, and its blacklist check queries dozens of DNSBLs at once. For "what is the state of this domain's mail and DNS right now," it is fast, thorough, and free.
Merlonix overlaps with a slice of what MXToolbox does — blacklist status, DNS records, certificate health — but from a different angle. MXToolbox is built around the on-demand lookup: you type a domain, you read the result. Merlonix is built around the continuous watch: it re-runs a set of checks on a schedule and alerts you when one of them changes, for every domain in a portfolio. This page is about where each fits.
What MXToolbox Gets Right
The Best Free Diagnostic Lookups
For a single point-in-time question, MXToolbox is hard to beat. Its blacklist tool checks a domain or IP against a large set of DNSBLs in one pass. Its SuperTool resolves MX, A, TXT, SPF, DMARC, and DKIM records and explains what each one means. When you are debugging a mail-delivery problem right now, this is the tool you reach for.
Email-Deliverability Depth
MXToolbox's centre of gravity is email. Its SPF, DMARC, and DKIM analysis, its message-header analyzer, and its Delivery Center are built around the deliverability problem specifically. If email deliverability is your primary concern, MXToolbox goes deeper on that domain than a general monitor does — and we do not claim to match that email-specific depth.
Widely Trusted
MXToolbox results are a common reference point. When you send a client an MXToolbox blacklist result, it is understood.
Where MXToolbox Stops for Portfolio Monitoring
Lookups Are Point-in-Time
The free SuperTool and blacklist checks are, by design, on-demand. You run them, you get an answer for that moment, and the tool does not remember the domain or re-check it. MXToolbox does offer paid continuous monitoring (Delivery Center) for blacklist and mail signals — but that is a separate, email-deliverability-focused product with its own pricing, not the free lookups most people know it for.
Email-Centric, Not Full-Stack
MXToolbox's monitoring is organised around mail and DNS. It does not continuously watch the things that take a website down independently of email: TLS certificate expiry and weak key material, DNSSEC signed→unsigned transitions, HTTP security-header regressions, or broken links and mixed content appearing on the site. A domain can be perfectly deliverable and still be serving an expired certificate or a page full of broken links.
Single-Owner, Not Multi-Client
MXToolbox is built for one operator checking their own (or a client's) domain. There is no client-account structure that lets an agency give each client a scoped view of their own monitoring, and no per-client reporting model. At portfolio scale, that means either one shared account or a manual per-domain lookup loop.
Results Are Diagnostic, Not Deliverable
MXToolbox output is a diagnostic readout. It is not formatted as a client-facing monthly report. For a team on a monitoring retainer, turning MXToolbox results into a client deliverable is manual work that recurs every month.
What Merlonix Provides Instead
Merlonix is the continuous, multi-signal, multi-client side of the same problem:
Continuous blacklist monitoring. Merlonix re-checks your domains against DNS blacklists on a schedule and alerts you when one lands on a list — and again when it is delisted — so you find out from an alert, not from a bounced-email complaint.
A full-stack watch, not just mail. Alongside blacklist status, Merlonix continuously monitors DNS record drift, DNSSEC integrity, TLS certificate expiry and key posture, HTTP security headers, domain registration and registrar-lock changes, and broken-link/mixed-content crawls. Each regression is an alert.
Email-auth posture, surfaced. Merlonix's free domain-health and security-header tools read SPF, DMARC, and MTA-STS posture so you can see a domain's spoofability at a glance. (For deep, email-specific deliverability analysis, MXToolbox remains the specialist — we are honest about that division.)
Portfolio and client structure. Every monitored domain lives in one place. For agencies, each client gets a scoped view, and monthly reports plus a branded audit PDF are produced as a by-product of monitoring — not assembled by hand from lookup results.
The honest division of labour: use MXToolbox for a fast, deep, one-off DNS/blacklist/email lookup — especially when the question is specifically about email deliverability. Use Merlonix when you want blacklist, DNS, DNSSEC, certificate, security-header, and broken-link status watched continuously across a whole portfolio, with alerts on regression and client-ready reports.
→ Try it now: free domain-health check (DNS, SSL, SPF/DMARC posture)
→ See also: DNSSEC monitoring · Broken-link & mixed-content monitoring · Domain-hijack / registrar-lock monitoring
→ Related: Merlonix vs SSL Labs — A Deep One-Time Scan vs. Continuous Monitoring