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Guerrilla Mail vs PostStack

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

APIGuerrilla MailNEW—PostStackNEW—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
AuthnoneapiKey
CORSyesno
HTTPSyesyes
Card requirednono
Commercial useunclearunclear
Data licenseUnverifiedUnverified
Free tierFree — limits not publishedFree tier — key may be required
Rate limitUnpublishedUnpublished
In directory since2026-07-052026-07-05
operationalpartialdownno data

Guerrilla Mail vs PostStack: common questions

Which is more reliable, Guerrilla Mail or PostStack?

On our scheduled checks, PostStack leads on measured uptime — Guerrilla Mail at —% versus PostStack 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 Guerrilla Mail and PostStack need an API key?

Guerrilla Mail needs no key, while PostStack requires a free API key. If you want to start calling without signup, reach for Guerrilla Mail first.

Can I call Guerrilla Mail and PostStack from the browser?

Only Guerrilla Mail is browser-friendly — it returns CORS headers over HTTPS. PostStack needs a server-side call or proxy, so factor that into which one fits a front-end project.

Are Guerrilla Mail and PostStack free for commercial use?

Guerrilla Mail has unclear commercial terms, and PostStack 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.