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SignGuard
Block burner emails before they drain your AI credits
Bots use disposable emails to farm your free tier — burning API credits, SMS costs, and server time. SignGuard scores every signup: disposable domains, typosquats, catch-alls, SMTP checks, domain age. 3 lines of code. Free tier, then $19/mo.
I'm Harshit - backend engineer. SignGuard is the first thing I've built on my own.
Why I built this?
Every time I saw a startup launch with free AI credits, I'd test their signup form with a mailinator.com or temp-mail.org address. It went through almost every time.
These are products giving away real GPU and API spend, wide open to a script that cycles 300 burner addresses over a weekend. Stripe just put numbers on it: abusive free trials up 6.2× in a year, and more than 1 in 6 signups at AI companies tied to multi-account abuse.
The fixes available were bad — $99/mo for an enterprise list-cleaning tool built for marketers, or a stale GitHub domain list that rotating providers bypass in a week. So I wrote my own engine and put it on PyPI. People kept asking for live checks, so it became an API.
What it does?
One API call on your signup route returns a 0–1.0 risk score and the signals behind it:
🔹 74,000+ disposable domains, continuously updated — rotating providers get caught without you maintaining a list 🔹 Typosquat detection for lookalikes like gmaiil.com 🔹 IDN homograph protection — Punycode-normalized, so a Cyrillic ɡmail.com can't slip past 🔹 Canonicalization — [email protected] resolves to one identity, so a single inbox can't farm unlimited trials 🔹 SMTP mailbox checks, catch-all detection, and domain age
Safe to run on your critical path
Non-blocking by design. If the cloud check is slow or unreachable, the SDK instantly switches to the bundled local engine in <1ms and returns UNKNOWN — so you never block a real paying customer.
Free for 200 signups/mo, no card required. The offline engine is MIT on PyPI forever.
Try it on yourself
Go sign up to your own product with a mailinator.com or yopmail.com address. If it goes through, you have this leak live right now.
What disposable trick has burned you the worst?
Tell me in the comments and I'll add it to the blocklist today.
— Harshit
About SignGuard on Product Hunt
“Block burner emails before they drain your AI credits”
SignGuard was submitted on Product Hunt and earned 2 upvotes and 1 comments, placing #121 on the daily leaderboard. Bots use disposable emails to farm your free tier — burning API credits, SMS costs, and server time. SignGuard scores every signup: disposable domains, typosquats, catch-alls, SMTP checks, domain age. 3 lines of code. Free tier, then $19/mo.
On the analytics side, SignGuard competes within API, Developer Tools, GitHub and Security — topics that collectively have 662.8k followers on Product Hunt. The dashboard above tracks how SignGuard performed against the three products that launched closest to it on the same day.
Who hunted SignGuard?
SignGuard was hunted by Harshit Jain. A “hunter” on Product Hunt is the community member who submits a product to the platform — uploading the images, the link, and tagging the makers behind it. Hunters typically write the first comment explaining why a product is worth attention, and their followers are notified the moment they post. Around 79% of featured launches on Product Hunt are self-hunted by their makers, but a well-known hunter still acts as a signal of quality to the rest of the community. See the full all-time top hunters leaderboard to discover who is shaping the Product Hunt ecosystem.
For a complete overview of SignGuard including community comment highlights and product details, visit the product overview.
Harshit Jain
Hey Product Hunt 👋
I'm Harshit - backend engineer. SignGuard is the first thing I've built on my own.
Why I built this?
Every time I saw a startup launch with free AI credits, I'd test their signup form with a mailinator.com or temp-mail.org address. It went through almost every time.
These are products giving away real GPU and API spend, wide open to a script that cycles 300 burner addresses over a weekend. Stripe just put numbers on it: abusive free trials up 6.2× in a year, and more than 1 in 6 signups at AI companies tied to multi-account abuse.
The fixes available were bad — $99/mo for an enterprise list-cleaning tool built for marketers, or a stale GitHub domain list that rotating providers bypass in a week. So I wrote my own engine and put it on PyPI. People kept asking for live checks, so it became an API.
What it does?
One API call on your signup route returns a 0–1.0 risk score and the signals behind it:
🔹 74,000+ disposable domains, continuously updated — rotating providers get caught without you maintaining a list
🔹 Typosquat detection for lookalikes like gmaiil.com
🔹 IDN homograph protection — Punycode-normalized, so a Cyrillic ɡmail.com can't slip past
🔹 Canonicalization — [email protected] resolves to one identity, so a single inbox can't farm unlimited trials
🔹 SMTP mailbox checks, catch-all detection, and domain age
Safe to run on your critical path
Non-blocking by design. If the cloud check is slow or unreachable, the SDK instantly switches to the bundled local engine in <1ms and returns UNKNOWN — so you never block a real paying customer.
Free for 200 signups/mo, no card required. The offline engine is MIT on PyPI forever.
Try it on yourself
Go sign up to your own product with a mailinator.com or yopmail.com address. If it goes through, you have this leak live right now.
What disposable trick has burned you the worst?
Tell me in the comments and I'll add it to the blocklist today.
— Harshit