MXToolbox has been around since 2003 and is one of the most widely-used free tools for email administrators and IT teams. If you've ever checked a blacklist, looked up an MX record, or verified SPF syntax, you've probably used it.
Brain is a different category of product. Rather than running one-off lookups, it continuously monitors your sending infrastructure and diagnoses failures when they occur. The comparison isn't really "which is better" — it's "which does the job you actually need done."
What MXToolbox does well
MXToolbox excels as an on-demand diagnostic utility. Its core strengths:
- Blacklist checking — quick check whether an IP or domain is listed on any of 100+ blacklists. Free, fast, comprehensive.
- DNS record lookup — inspect MX, SPF, DKIM, DMARC, PTR, and A records in a clear interface. Invaluable for debugging authentication setup.
- MX record health — verify mail server configuration and catch common misconfigurations.
- SMTP diagnostics — test SMTP connectivity, banner checks, and TLS support.
- Deliverability score — the paid Deliverability product gives a snapshot score with recommendations.
For IT teams setting up email infrastructure, troubleshooting a one-off issue, or verifying configuration after a DNS change, MXToolbox is a solid pick. It's free for basic lookups and the paid plans are reasonably priced.
Where Brain goes further
MXToolbox shows you the state of your infrastructure at the moment you run a check. Brain monitors your infrastructure continuously and responds when something changes.
Brain's distinctive capabilities:
- Continuous signal monitoring — 30+ signals monitored simultaneously across Gmail, Outlook, and Yahoo, no manual action required.
- Real-time reputation data — Google Postmaster, Microsoft SNDS, and Sender Score ingested continuously, not on demand.
- Automated incident detection — the Signal Engine raises incidents the moment signals deviate from baseline.
- Root-cause analysis — the RCA Inspector and Causal Graph trace why a deliverability event happened, not just that it happened.
- Pattern recognition — recurring failure signatures across incidents, surfaced for permanent fixes.
- Resolution tracking — Outcome Tracker confirms whether a fix actually worked by monitoring signal recovery.
See Brain's full intelligence layer →
Feature comparison
| Feature | InboxStack Brain | MXToolbox |
|---|---|---|
| Primary function | Continuous deliverability monitoring | On-demand DNS & email diagnostics |
| Monitoring | Real-time 24/7 automated | Manual checks only |
| Automated alerts | Yes — Signal Engine raises incidents | Limited — paid-plan monitoring alerts |
| Root-cause analysis | Yes — Causal Graph + RCA Inspector | No |
| Reputation monitoring | Continuous Postmaster, SNDS, Sender Score | Snapshot in Deliverability product |
| Authentication checks | Ongoing DMARC/DKIM/SPF health | On-demand DNS lookups |
| Blacklist monitoring | Continuous across major RBLs | On-demand 100+ blacklists (free) |
| MBP coverage | Gmail, Outlook, Yahoo — live data | Generic — not MBP-specific |
| Incident management | War Room, Resolution Center | No |
| Free DNS lookups | Free DNS Checker for ad-hoc use | Yes — excellent free tool |
| Pricing | From $49/month — see plans | Free basic / paid from ~$129/month |
| Best for | Senders who need proactive continuous protection | IT teams doing one-off DNS diagnostics |
Pricing
MXToolbox's free tier covers basic lookups and is genuinely useful without spending anything. The paid Deliverability plans start around $129/month and add monitoring alerts, scoring, and additional checks.
Brain starts at $49/month (Radar) for real-time monitoring, $99/month (Brain) for the full Signal Engine + RCA Inspector + Resolution Center, and $349/month (Command) for unlimited ESP connectors, multi-tenant workspaces, and white-label intelligence. Full pricing →
Which one do you need?
Use MXToolbox if you need to:
- Quickly check whether an IP is blacklisted
- Look up and validate DNS records (MX, SPF, DKIM, DMARC, PTR)
- Troubleshoot a one-off mail server configuration issue
- Test SMTP connectivity to a mail server
- Run a free email infrastructure health check
Use Brain if you need to:
- Know when your deliverability is degrading — before your recipients tell you
- Understand why inbox placement dropped, not just that it did
- Monitor multiple domains across Gmail, Outlook, and Yahoo continuously
- Manage deliverability incidents systematically with a team
- Confirm that a fix actually resolved the underlying problem
The verdict
MXToolbox is a valuable free tool for one-off DNS diagnostics and blacklist checks — earned its place in every email administrator's bookmarks. Brain addresses a fundamentally different problem: continuous, proactive deliverability intelligence that catches issues before they cost you inbox access. For teams that send at volume and can't afford to learn about deliverability failures retroactively, Brain is what you need.
Still weighing options? How to choose an email deliverability tool →