Bulk Gmail Verification – How Are Services Checking Valid/Live Accounts?

Hey guys,

I’m looking for some insight on how large-scale Gmail checking (existence / live / valid status) is typically done.

I’ve noticed there are quite a few services on the market offering bulk Gmail verification — checking whether an account exists, is alive, or still usable. I’m trying to understand the underlying methods behind this.

So far I’ve experimented with SMTP-based verification, but the results aren’t very reliable (catch-alls, greylisting, and inconsistent responses make it hard to trust).

I’m curious:

• What methods are commonly used nowadays for Gmail validation at scale?
• Are people relying on web-based flows (login / recovery endpoints), APIs, or something else?
• How do these services avoid rate limits or detection when checking in bulk?
• Is there any relatively stable approach that works better than SMTP?

Not looking for anything shady — just trying to understand the technical side and improve accuracy.

Appreciate any insights or directions

SMTP doesn't work for Gmail by design — Google returns 250 OK for everything to prevent harvesting, catch-all is just the symptom. The two methods that actually work: the password recovery flow (hit the account recovery endpoint and check whether Google confirms the address exists vs returns "couldn't find your account"), and the signup form flow (POST to accounts.google.com/signup and check for "that username is taken" vs success). Recovery endpoint is faster but Google rate-limits it aggressively — you need rotating residential proxies, randomized delays around 2–4 seconds, and low concurrency per IP. Signup form is slower but more stable at scale. Any service doing "bulk Gmail check" is using one of these two under the hood; if they claim SMTP they're lying or their results are garbage.