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mailboxlayer vs PostStack

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

APImailboxlayerNEW—PostStackNEW—
Uptime · 30d
Uptime · 90d—%—%
Uptime · 30d—%—%
P50 · ms——
P95 · ms——
AuthapiKeyapiKey
CORSnono
HTTPSyesyes
Card requirednono
Commercial useunclearunclear
Data licenseUnverifiedUnverified
Free tierFree tier — key may be requiredFree tier — key may be required
Rate limitUnpublishedUnpublished
In directory since2026-07-052026-07-05
operationalpartialdownno data

mailboxlayer vs PostStack: common questions

Which is more reliable, mailboxlayer or PostStack?

On our scheduled checks, PostStack leads on measured uptime — mailboxlayer 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 mailboxlayer and PostStack need an API key?

Both ask you to authenticate — mailboxlayer uses an API key and PostStack uses an API key. Each key is free to obtain; the Auth and Card-required rows above spell out the signup terms.

Can I call mailboxlayer and PostStack from the browser?

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

Are mailboxlayer and PostStack free for commercial use?

mailboxlayer 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.