## Why It Matters

Throwaway inboxes — mailinator, 10minutemail, guerrillamail, temp-mail — let anyone sign up, submit a report, or claim a bounty without a real, reachable address. When you need to decide whether an address is worth trusting, guessing from the domain name doesn't scale: new disposable providers appear constantly, and some hide behind fresh front-domains. The Email Checker gives a responder a one-glance verdict from a single lookup.

## What It Does

Paste one email address — or a whole list, one per line — and each gets a verdict:

- **Disposable** — the address belongs to a known throwaway provider.
- **Looks legitimate** — nothing flags it as disposable.
- **Invalid** — the address isn't a structurally valid email at all.

Each result also shows *why* (known disposable domain, disposable mail server, or a formatting problem), the domain, and whether the domain has mail servers.

### How the verdict is reached

| Signal | What it checks |
|--------|----------------|
| Format | Structural validity of the address (regex) |
| Blocklist | Whether the domain is on a curated, daily-refreshed list of disposable-email providers |
| Mail-server fingerprint | Whether the domain's MX servers belong to a known disposable provider — catching brand-new front-domains the blocklist hasn't listed yet |

> [!NOTE]
> "Looks legitimate" means nothing flagged the address as disposable — not that the inbox has been proven to exist or that mail will be delivered. Absence of a disposable signal isn't a delivery guarantee.

> [!TIP]
> Turn off **Check mail servers** for an instant, blocklist-only answer with no DNS lookup. Leave it on to also catch fresh throwaway domains whose mail servers give them away.

## Screening an Email

Open the [Email Checker](/tools/email_check) page. Any signed-in account member can use it.

1. Paste one address, or a list separated by new lines, spaces, or commas.
2. Choose whether to check mail servers (on by default).
3. Submit — a verdict card renders inline for each address.

## Where the Data Comes From

The disposable-domain blocklist is the curated, low-false-positive [`disposable-email-domains`](https://github.com/disposable-email-domains/disposable-email-domains) list, refreshed daily into Kit. It deliberately excludes privacy relays and large regional providers (Apple Hide My Email, DuckDuckGo/Firefox Relay, and the like) so real, permanent addresses aren't mistaken for throwaways. The mail-server fingerprint uses public DNS. The tool never touches or exposes your account data, and nothing you screen is persisted.

## Limits

| Limit | Value |
|-------|-------|
| Batch size | Up to 25 addresses per screening; the rest are noted and can be screened separately |
| Mail-server check | A DNS lookup per address, bounded by a short timeout — an unreachable resolver reports mail servers as "not checked" rather than hanging |
| Coverage | The blocklist catches the vast majority of disposable providers; the mail-server fingerprint extends it to fresh front-domains, but a brand-new provider with its own infrastructure can still slip through until the list catches up |

## Quick Checklist

- [ ] Open the [Email Checker](/tools/email_check) page
- [ ] Paste one address, or up to 25 at once
- [ ] Leave **Check mail servers** on to catch fresh throwaway domains
- [ ] Treat a "disposable" verdict as a reason to require a real address before you trust the signup or report