MXToolbox has run since 2004 and is the reference for ad-hoc DNS and email diagnostics. Their free SuperTool covers a wide breadth of record types — DMARC, SPF, DKIM, MX, blacklist checks, header analysis, and more. Many engineers have a tab open to MXToolbox the way they have one open to a man page.
MailerMonk overlaps with MXToolbox on the free DNS tools (DMARC, SPF, DKIM, MX, blocklist) but is built around a different problem: catching deliverability regressions before customers complain. MXToolbox's paid tier offers monitoring too, but it's enterprise-priced and the alerting feels bolted onto the lookup tool. MailerMonk starts at the monitoring use-case and treats the free tools as the funnel into it.
Feature comparison
| Feature | MailerMonk | MXToolbox |
|---|---|---|
| Free single-shot DMARC / SPF / DKIM / MX checks | Yes | Yes |
| Free blocklist check | Yes | Yes |
| Continuous DMARC report ingestion + parsing MXToolbox includes this in their Delivery Center plan. | Yes | Yes |
| Inbox-placement monitoring (Gmail Postmaster Tools sync) | Yes | No |
| Real-time alerts for blocklist / DMARC / reputation drops | Yes | Yes |
| Header analyzer / message tracer | No | Yes |
| Dedicated SMTP test sender | No | Yes |
| Multi-domain agency view MXToolbox supports multiple domains but the UI is not agency-oriented. | Yes | Partial |
| Browser extension | Yes | No |
Choose MXToolbox when…
- You want a one-stop shop for ad-hoc email + DNS diagnostics — header analysis, NS lookups, SMTP traceroute, etc.
- You're already running enterprise-tier tooling and the cost difference is irrelevant.
- You need the breadth of record types and lookups MXToolbox covers (blacklist coverage alone is dozens of lists).
Choose MailerMonk when…
- You're a B2B founder, sales team, or agency where the question is 'is my outbound mail landing?', not 'what's the SMTP banner of mx1.example.com?'
- You want continuous monitoring at SMB pricing, not enterprise pricing.
- You want Gmail Postmaster Tools sync and inbox-placement signal, not just DNS-record diffs.
Pricing
MXToolbox is free for ad-hoc lookups; their monitoring (Delivery Center) is enterprise-tier and quoted on request. MailerMonk's monitoring starts at SMB pricing.
See MXToolbox pricing →