---
title: "How to Block Disposable Emails at Signup (Free Temp Email Checker)"
description: "Stop throwaway signups before they bounce, burn free trials, and tank sender reputation. Use Reloop's free temp email checker: ~210k disposable domains, no SMTP probing."
canonical: "https://reloop.sh/blog/block-disposable-emails-at-signup"
last-updated: "2025-11-18"
---

# How to Block Disposable Emails at Signup (Free Temp Email Checker)

> For the site documentation index, see [llms.txt](/llms.txt). Docs index: [llms-docs.txt](/llms-docs.txt). Marketing corpus: [llms-full.txt](/llms-full.txt). Docs corpus: [llms-full-docs.txt](/llms-full-docs.txt). Product skill: [skill.md](/skill.md). Prefer markdown URLs (append `.md`) when available.

> Stop throwaway signups before they bounce, burn free trials, and tank sender reputation. Use Reloop's free temp email checker: ~210k disposable domains, no SMTP probing.
Source: https://reloop.sh/blog/block-disposable-emails-at-signup
Published: 2025-11-18
Temporary inboxes are useful for privacy. They are expensive for anyone who sends email for a living.

A disposable address often dies within an hour. Every message you send after that is a hard bounce. Sustained bounce rates are how mailbox providers decide your domain belongs in spam, for every recipient, not just the throwaway ones.

If you run a SaaS free tier, a newsletter, or a product waitlist, disposable signups also inflate your metrics and farm your credits. The fix is simple: check the address at signup, before it lands in your database.

This guide covers when to block temporary emails, how a [temp email checker](/tools/temp-email-checker) works, and how to wire Reloop's free public API into a registration flow.

## What a temp email checker actually checks

A temp email checker (also called a disposable email detector) answers one question: *is this address from a known throwaway provider?*

Reloop's [free Temp Email Checker](/tools/temp-email-checker) does more than a domain string match. On each request it:

1. **Parses RFC syntax**: malformed input never reaches the catalogue or DNS.
2. **Matches ~210,000 disposable providers**, including Mailinator, Yopmail, Temp-Mail, Guerrilla Mail, and 10MinuteMail, plus wildcard suffixes for providers that mint endless subdomains.
3. **Flags role prefixes**: `info@`, `billing@`, `support@` are shared inboxes, not burners. They are reported separately so you can apply your own policy.
4. **Looks up MX records**: confirms the domain publishes a mail exchanger. That is routing evidence, not proof the mailbox exists.
5. **Never opens an SMTP session**: no mailbox probe, no stored addresses, no account required.

A disposable verdict means the domain is on the catalogue. A clear verdict means "not currently known to be disposable." New temp-mail services appear constantly, so treat the check as a strong signal, not a lifetime guarantee.

For a deeper walkthrough of detection methods, see [how to check if an email is disposable](/blog/disposable-email).

## Why disposable emails damage deliverability

Mailbox providers track bounce rate as a core reputation signal. Industry guidance keeps hard bounces well under ~2%. Throwaway inboxes make that threshold easy to miss:

- The mailbox is deleted minutes or hours after signup.
- Your welcome email, password reset, or drip sequence hard-bounces.
- Those failures are scored against your sending domain and IP.
- Reputation damage spreads to legitimate recipients: password resets and receipts start landing in spam.

That is the same chain that ends with [emails in the spam folder](/blog/why-emails-land-in-spam-fix). Authentication (SPF, DKIM, DMARC) and [IP warming](/blog/ip-warming-guide) matter, but none of them fix a list full of dead temporary addresses.

Prevention sits in front of bounce handling. Validate at signup, then suppress hard bounces immediately so dead temporary addresses never get a second send.

## Signup abuse patterns a checker stops

Deliverability is one reason to block. Product abuse is the other.

| Pattern | What happens without a check | What a temp email checker does |
| --- | --- | --- |
| Free trial farming | Unlimited throwaway accounts, unlimited trials | Block at registration when `isDisposable` is true |
| Coupon / referral fraud | Same offer claimed with a new burner each time | Reject or flag before the promotion is applied |
| Waitlist inflation | Fake demand, useless launch emails | Keep the list honest before you send |
| Newsletter padding | Open rates collapse; engagement signals look terrible | Suppress burners before the first campaign |
| Multi-account bots | Shared disposable domains scale abuse cheaply | Catch the domain family, including wildcard providers |

Role addresses (`admin@`, `sales@`) are a different problem: they are real and persistent, but shared. Reloop flags them separately so you can require a personal inbox without treating Gmail or Outlook as disposable.

## When to block vs when to flag

Blocking every temporary email is not always the right product decision.

**Block at signup when:**

- You offer a free trial, freemium tier, or usage credits
- You run new-customer discounts or referral rewards
- Fake accounts distort activation or retention metrics
- You send transactional email and cannot afford bounce spikes

**Flag or allow when:**

- Privacy-sensitive audiences expect anonymous access
- The flow is feedback, bug reports, or one-off downloads
- You will suppress later rather than reject at the door

A practical middle path: block disposable domains on paid or trial signup, and on newsletter forms either soft-warn or accept then suppress before campaigns. Pair the check with email confirmation and CAPTCHA so you are not relying on a single signal.

## How to check an address with Reloop (free)

### Option 1: Use the web tool

Paste an address into the [Reloop Temp Email Checker](/tools/temp-email-checker). You get a verdict, disposable match details, role and free-provider flags, MX hosts, confidence, and risk score instantly, with no signup.

Examples:

- `alex@gmail.com`: deliverable consumer mailbox (free provider, not disposable)
- `you@mailinator.com`: disposable
- `demo@yopmail.com`: disposable

### Option 2: Call the public API at signup

The checker is a thin wrapper over one public endpoint. No API key. No account. Rate limited per IP, so keep it to signup-time checks, not bulk scrubbing.

`POST https://reloop.sh/api/tools/v1/temp-email-checker`

<TempEmailCheckerCodeSamples />

A throwaway mailbox returns `"verdict": "disposable"` and `"isDisposable": true`:

```json
{
  "input": "you@mailinator.com",
  "kind": "email",
  "domain": "mailinator.com",
  "verdict": "disposable",
  "isValidSyntax": true,
  "isDisposable": true,
  "disposableMatch": {
    "kind": "exact",
    "domain": "mailinator.com"
  },
  "isAllowlisted": false,
  "isRoleAddress": false,
  "isFreeProvider": false,
  "signals": {
    "syntax": "pass",
    "disposable": "fail",
    "role": "pass",
    "freeProvider": "pass"
  },
  "mxRecords": ["spool.mailinator.com"],
  "confidence": 0.99,
  "riskScore": 0.95,
  "flags": ["DISPOSABLE_DOMAIN", "PUBLIC_INBOX_DETECTED"]
}
```

Reject or challenge the signup when `isDisposable` is `true`. Optionally treat high `riskScore` or role addresses as soft warnings.

Need to clean an existing list rather than gate one registration? Use Reloop's free [email validator](/tools/email-validator) for syntax, disposable detection, live MX, and CSV cleaning (up to 1,000 rows) in one pass. For production volume and policy controls, see [email validation](/features/email-validation) on Reloop.

## Layer checks that protect reputation end to end

Disposable detection is one layer. Strong signup hygiene stacks several:

1. **Temp / disposable check**: [Temp Email Checker](/tools/temp-email-checker) at account creation
2. **List hygiene before campaigns**: [Email Validator](/tools/email-validator)
3. **Authentication health**: [SPF, DKIM & DMARC checker](/tools/auth-checker) and the [setup guide](/blog/spf-dkim-dmarc-setup-guide)
4. **Inbox placement tests**: [Deliverability tester](/tools/deliverability-tester)
5. **Blocklist monitoring**: [IP & domain blocklist checker](/tools/blocklist-checker)
6. **Transactional quality**: keep password resets and receipts on a dedicated subdomain with proper auth so the mail you do send deserves the inbox

Reloop is open-source email infrastructure. You can use the hosted tools, call the public checker API, or [run Reloop yourself](/blog/why-we-open-sourced-email-infrastructure) when you want the same checks on your own servers.

## Frequently asked questions

### Is blocking disposable emails legal?

Yes. Temporary email services are legal for users. Choosing not to accept them on your product is a normal terms-of-service and fraud-prevention decision, in the same category as blocking known bot ASNs or requiring phone verification.

### Will a temp email checker catch brand-new throwaway domains?

List-based detection only knows what is on the catalogue. Reloop resyncs roughly every two hours across ~210,000 providers, which catches most new services quickly, but a brand-new domain can slip through until it is listed. Combine the check with confirmation email and rate limits.

### Does Reloop prove the mailbox exists?

No. MX lookup shows mail can be routed to the domain. Reloop never probes the mailbox over SMTP. That keeps the tool fast, privacy-friendly, and suitable for a public endpoint.

### Is Gmail or Outlook disposable?

No. Free consumer providers are persistent. Reloop may flag them as free providers so you can apply your own rules; they are not treated as throwaway.

### Temp email checker vs email validator: which should I use?

Use the [temp email checker](/tools/temp-email-checker) to block burners at signup (single address, public API). Use the [email validator](/tools/email-validator) when you need bulk CSV cleaning, fuller health scoring, and export for campaign hygiene.

## Next step

Run a known throwaway address through the [free Temp Email Checker](/tools/temp-email-checker), then wire the same check into your registration handler with the public API above.

If you are already sending through Reloop or evaluating open-source transactional email, start free at [reloop](https://reloop.sh) and keep disposable addresses out of the path that builds your sender reputation.