shipapis
StarSubmit an APISubmit API

MailCheck.ai vs PostStack

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

APIMailCheck.aiHEALTHY93PostStackHEALTHY87
Uptime · 30d
Uptime · 90d93.1%100%
Uptime · 30d93.3%100%
P50 · ms2721066
P95 · ms8421890
AuthnoneapiKey
CORSyesno
HTTPSyesyes
Card requirednono
Commercial useunclearunclear
Data licenseUnverifiedUnverified
Free tierFree — limits not publishedFree tier — key may be required
Rate limit5 req/window · 4 remainingUnpublished
In directory since2026-07-052026-07-05
operationalpartialdownno data

MailCheck.ai vs PostStack: common questions

Which is more reliable, MailCheck.ai or PostStack?

On our scheduled checks, PostStack leads on measured uptime — MailCheck.ai at 93.1% versus PostStack at 100% over 90 days. These are our own probe results, not provider claims; the uptime bars above show the day-by-day record for both.

Which is faster, MailCheck.ai or PostStack?

MailCheck.ai has the lower median latency in our checks — MailCheck.ai responds in 272 ms versus PostStack at 1066 ms (P50). Tail latency (P95) is in the table above; for most workloads the median is the number that shapes how the API feels.

Do MailCheck.ai and PostStack need an API key?

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

Can I call MailCheck.ai and PostStack from the browser?

Only MailCheck.ai 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 MailCheck.ai and PostStack free for commercial use?

MailCheck.ai 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.