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MailboxValidator Free Email Checker vs RSQ API

Same instrument, two spec sheets — measured, not claimed.

APIMailboxValidator Free Email CheckerNEW—RSQ APINEW—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
AuthapiKeynone
CORSnoyes
HTTPSyesno
Card requirednono
Commercial useunclearunclear
Data licenseUnverifiedUnverified
Free tierFree tier — API key requiredFree — limits not published
Rate limitUnpublishedUnpublished
In directory since2026-07-052026-07-05
operationalpartialdownno data

MailboxValidator Free Email Checker vs RSQ API: common questions

Which is more reliable, MailboxValidator Free Email Checker or RSQ API?

On our scheduled checks, RSQ API leads on measured uptime — MailboxValidator Free Email Checker at —% versus RSQ API at —% over 90 days. These are our own probe results, not provider claims; the uptime bars above show the day-by-day record for both.

Do MailboxValidator Free Email Checker and RSQ API need an API key?

RSQ API needs no key, while MailboxValidator Free Email Checker requires a free API key. If you want to start calling without signup, reach for RSQ API first.

Can I call MailboxValidator Free Email Checker and RSQ API from the browser?

Neither sends browser-friendly CORS headers reliably, so call MailboxValidator Free Email Checker and RSQ API from a server or proxy rather than client-side. The CORS and HTTPS rows above show exactly what we detected for each.

Are MailboxValidator Free Email Checker and RSQ API free for commercial use?

MailboxValidator Free Email Checker has unclear commercial terms, and RSQ API has unclear commercial terms. We track service terms and the data license as separate fields — see the Commercial use and Data license rows above, and confirm both before shipping either in a paid product.