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

Stop throwaway signups before they bounce, burn free trials, and tank sender reputation.

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 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 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.

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. Authentication (SPF, DKIM, DMARC) and IP warming 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.

Free trial farming

Without a check: unlimited throwaway accounts, unlimited trials.

With a checker: block at registration when isDisposable is true.

Coupon / referral fraud

Without a check: the same offer claimed with a new burner each time.

With a checker: reject or flag before the promotion is applied.

Waitlist inflation

Without a check: fake demand and useless launch emails.

With a checker: keep the list honest before you send.

Newsletter padding

Without a check: open rates collapse and engagement signals look terrible.

With a checker: suppress burners before the first campaign.

Multi-account bots

Without a check: shared disposable domains scale abuse cheaply.

With a checker: 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. You get a verdict, disposable match details, role and free-provider flags, MX hosts, confidence, and risk score — instantly, with no signup.

Examples:

• [e-mail] — deliverable consumer mailbox (free provider, not disposable)
• [e-mail] — disposable
• [e-mail] — 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 — keep it to signup-time checks, not bulk scrubbing.

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

cURL

curl -X POST https://reloop.sh/api/tools/v1/temp-email-checker \
  -H "Content-Type: application/json" \
  -d '{"email": "[e-mail]"}'

JavaScript

// No SDK, no API key — it is a plain POST.
const res = await fetch(
  "https://reloop.sh/api/tools/v1/temp-email-checker",
  {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({ email: "[e-mail]" }),
  },
);

const result = await res.json();

Python

# pip install requests
import requests

result = requests.post(
    "https://reloop.sh/api/tools/v1/temp-email-checker",
    json={"email": "[e-mail]"},
).json()

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

{
  "input": "[e-mail]",
  "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 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 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 at account creation
2. List hygiene before campaigns — Email Validator
3. Authentication health — SPF, DKIM & DMARC checker and the setup guide
4. Inbox placement tests — Deliverability tester
5. Blocklist monitoring — IP & domain 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 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 — 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 to block burners at signup (single address, public API). Use the 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, 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.sh and keep disposable addresses out of the path that builds your sender reputation.

Originally published on the Reloop blog.