Comparison
MXToolbox is the lookup engineers already trust. Use it when you want the widest blacklist sweep or SMTP diagnostics. Use Inbox Watch when you want that style of check on a schedule, plus a verdict tied to cold-email sending.
Their site: mxtoolbox.com/
| Topic | MXToolbox | Inbox Watch |
|---|---|---|
| Blacklists | A large public blocklist set on the SuperTool. | The lists named on the methodology page. Spamhaus is not queried. A refusal or an unrecognized return code is unavailable, not a listing. |
| How often | When you run the lookup, unless you buy their monitoring. | Hourly for domains on a paid plan, including DNS-only watches. |
| Cold-email stats | Not part of the lookup. | Bounce and reply rates from Instantly or Smartlead when a key is connected. |
| Result page | A diagnostic report for operators who already know DNS. | A plain-English verdict, the records, and the fix. The URL is shareable. |
| What we will not claim | The broader blacklist coverage. | We do not say we check more lists than MXToolbox. We check fewer, on purpose, and we say which ones. |
MXToolbox checks far more blacklists than we do, and it includes SMTP, DNS, and DMARC-report tools we do not have. Their public SuperTool is a one-shot lookup. Ongoing monitoring is a separate MXToolbox product. We query NordSpam, LashBack UBL, UCEPROTECT Level 1, PSBL, Mailspike, and s5h. We do not query Spamhaus, SURBL, SpamCop, or Barracuda. Spamhaus is a link to their own checker.
Inbox Watch repeats the check every hour, emails you when authentication breaks or a watched list hits, and, with an API key, compares bounce and reply rates with the domain's own baseline. The Monday note says keep, rest, or replace. MXToolbox does not read Instantly or Smartlead.