What Are Disposable Emails (And Why They Break Your Signup Funnel)

A disposable email address is a temporary inbox that a visitor can create in one click, use once, and abandon. Services like tempmail, 10minutemail and mailinator hand out thousands of these per minute. The address is syntactically perfect, the domain has valid MX records, and a confirmation email will actually arrive — which is exactly why naive validation never catches them.

Why they hurt more than they look

• Trial abuse. One person becomes fifty free accounts.
• Broken metrics. Activation, retention and churn are computed on ghosts.
• Deliverability damage. Temporary inboxes expire, bounces climb, sender reputation falls.
• Moderation load. Spam comments and fake reviews almost always ride in on throwaway domains.

What actually detects them

Regex only proves the shape of the string. MX lookups only prove that mail can be delivered. The reliable signal is the domain itself: throwaway providers reuse a finite, well-known set of domains. Matching against a curated blocklist is the fastest and most accurate check you can run at signup.

SpamNull ships that dataset with the package — 215,822 usable domains after whitelist filtering — and resolves a lookup entirely inside your own process:

import isSpam from "spamnull";

isSpam("user@tempmail.com"); // true
isSpam("user@gmail.com");    // false

The whitelist matters as much as the blocklist

Raw blocklists scraped from the internet routinely include Gmail, Outlook and regional providers, which means real customers get rejected. SpamNull strips known-good providers before shipping the dataset. More on that trade-off in our guide to avoiding false positives.

Where to put the check

Signup, waitlist forms, comment endpoints, coupon redemption and password reset are the highest-value places. See how to block disposable emails at signup for a copy-paste implementation, and self-hosted vs API validation for why a local lookup beats a network call on those hot paths.

$ npm install spamnull