Try the free tool: Check an address with BillionVerify's disposable email detection tool before it enters your signup flow or contact database. The result helps you decide whether to accept, review, or block the address.
A temp mail address stays unnoticed only until a checker examines the right signal. Sites compare the domain with a list of disposable email domains. They also read its mail server records and its age, and they watch how it is used. This guide explains each signal and why an undetected result does not last. It also covers what to do when a real address is flagged.
BillionVerify does not run a temp mail service. We build email verification tools and publish a public repository that lists disposable email domains. Every fact below comes from that repository, public DNS lookups or vendor documentation, read on October 27, 2026.
Key facts (checked October 2026):
- The BillionVerify/disposable repository on GitHub held 220,601 domains on October 27, 2026, and its README says they are merged from nine community lists.
- Guerrilla Mail's homepage menu offered 11 domains in October 2026, and all 11 appear in that list.
- A public DNS lookup in October 2026 showed guerrillamail.com and sharklasers.com using one shared mail host, mail.guerrillamail.com.
- ZeroBounce's validate API documentation lists domain_age_days, mx_found and an alias_address sub-status among its result fields.
- RFC 9083 defines a registration event for domain lookups, so the date a domain was registered is public record.
Why Do Websites Detect Temp Mail?
A site that asks for an email address wants to reach you later. A temporary email inbox that vanishes within an hour breaks that plan. Four problems come up most often:
- Fake signups: accounts nobody will use inflate the user count.
- Repeat offers: one person claims the same trial or coupon again and again.
- No follow-up: receipts, security notices and password resets go nowhere.
- Weak lists: inboxes that never open mail drag down engagement.
So the form runs a temp mail detector before it accepts the address. A failed check ends in a message that rejects the address. The sections below show what the check looks at.
How Do Websites Check for Temporary Email?
Most checkers combine several signals. No single signal catches every address.
| Signal | What the checker looks at | Where it falls short |
|---|---|---|
| Domain list | The domain after the @ sign, matched against disposable email domains | Misses a domain no list has recorded yet |
| Mail host (MX) | Which server receives the domain's mail | Needs a known disposable host to compare with |
| Domain age | How recently the domain was registered | A new business domain looks the same |
| Alias and relay | Whether it only forwards mail to another mailbox | Many people use relays for privacy, not abuse |
| Signup behavior | IP address, timing and volume of signups | Only the site itself sees this data |
Domain Lists
A domain list is the main method. The checker takes everything after the @ sign and looks it up. An embedded list needs no network call, so the lookup is quick.
BillionVerify's open list shows how it works. Its README gives one rule order: exceptions first, then an exact match, then wildcard suffixes. A wildcard entry such as *.foo.example matches foo.example and every subdomain under it. An exceptions list names domains that are never flagged.
Screenshot: the BillionVerify/disposable page on GitHub. The newest commit is an hourly update that added two domains.
Mail Server Records
Every domain publishes MX records that name the servers receiving its mail. A temporary email service often points many domains at one mail host. Anyone can read those records:
$ dig +short MX guerrillamail.com 0 mail.guerrillamail.com. $ dig +short MX sharklasers.com 0 mail.guerrillamail.com. $ dig +short MX yopmail.com 1 smtp.yopmail.com. $ dig +short MX yopmail.fr 10 smtp.yopmail.com.
Two names, one host. A checker that knows the host can treat any other domain pointing at it as a suspect. ZeroBounce's documentation shows that at least one vendor reads this data, because its results include mx_found and mx_record.
Domain Age
A registration date is public. RDAP, the registry lookup protocol described in RFC 9083, includes a registration event for it. ZeroBounce's API returns the result as domain_age_days.
Age is a hint, not proof. Every real company domain was new once, so a checker should weigh it next to other signals.
Aliases and Relays
An alias forwards mail to a real mailbox. ZeroBounce reports alias_address as a sub-status separate from disposable, so some checkers treat the two cases differently.
Lists are less careful. The BillionVerify list includes relay.firefox.com, privaterelay.appleid.com, simplelogin.com, addy.io and duck.com. These services hide a real address, and people use them for privacy. A site that rejects every entry on a list rejects those users as well.
Signup Behavior
Some signals never appear in the address. ZeroBounce's validate API accepts an ip_address parameter, described as the IP the email signed up from. A burst of signups from one IP, each with a new email address, stands out even when every address looks clean.
Why Undetectable Temp Mail Claims Do Not Last
A page that promises undetectable temp mail describes one result. It says nothing about the next list update or the next site. Four facts explain why.
"Temp Mail Not Detected" Is One Snapshot
A claim of "temp mail not detected" means one checker, one list and one day. Another site runs another checker. Both can be right at the same time.
Lists Change Every Hour
The open list pulls from its nine sources every hour. A domain added upstream can appear within the hour, so a domain that passes today can fail tomorrow.
One Service Runs Many Domains
A single service can offer more than ten domains. Guerrilla Mail lists 11 in its menu, and the open list already holds all 11.
Screenshot: Guerrilla Mail with the domain menu expanded.
Sites Check Again Later
A signup is not the only checkpoint. A site can re-check an address before a purchase or an upgrade, using fresher data than it had at signup.
We do not list which services slip through, and we do not explain how to avoid these checks. A site decides which addresses it accepts.
If a Site Rejects Your Real Email Address
A real address is sometimes flagged too. Three causes are common:
- A relay or forwarding address. Privacy relays appear on some lists, as shown above.
- A new domain. A company that registered its domain last month can trip an age check.
- An old list. The site's list may contain a domain that has changed hands.
Sign up with a mailbox you own whenever the account matters. If a real work address is rejected, write to the site's help desk and name the address you used. The team may be able to clear a false flag.
How to Block Disposable Email on Your Signup Form
If you run a signup form, you can check each address before you accept it.
Check at the Form
The best moment is while the user is still on the page. The check runs when the form is submitted. A flagged email address gets an instant message asking for a permanent one.
For a quick check before building rules, test a sample address with the disposable email detector. It provides a practical reference point for how temporary-email risk should appear in your registration workflow.
Use the Open-Source List
The library at github.com/BillionVerify/disposable is free. Per its README, it offers Go and Rust libraries and a Go command-line tool. The domain list is embedded in the program, so a lookup makes no network call.
if disposable.IsEmail("user@mailinator.com") {
// refuse, throttle, or tag as low-trust
}
The README also documents a hosted check that does not use credits. It performs only the domain lookup and does not call SMTP or MX servers. Our release post explains the list in more detail.
Block or Flag
A hard block is not always right. Many teams explain the rule and ask for a lasting address. Others let the signup through and tag it as low trust. Do not block Gmail or Outlook because they are free. Neither domain is on the list, because both are real mailboxes.
Keep your own exceptions. The library lets you hot-swap the table and add domains that must never be flagged, such as a customer's legitimate relay address.
Re-check Your Existing List
Disposable addresses may already sit in your database. Bulk email verification flags them so you can segment them before the next campaign. Disposable detection is separate from catch-all detection: a catch-all domain accepts any address, and it is not always disposable.
How to Verify a Temp Email Address
To check one email address, paste it into BillionVerify's free temp mail checker. A temp mail detector like this answers one question: is the domain disposable? It does not bury that answer in a long risk report.
For a full check, use the email verifier. It tests syntax, DNS, MX records and SMTP, as our guide to email verification explains. Valid and invalid results cost one credit each, unknown results cost nothing, and a recheck within 24 hours is free. Every account gets 20 free credits on each day you use it, up to 600 a month. They never expire and need no credit card.
An unfamiliar domain in a lead list may need more than a flag. A reverse email lookup shows the organization behind it. Phone fields have the same problem with virtual numbers, and a free phone number validator shows the line type.
FAQs
Why is my temp mail not detected on one site but blocked on another?
Each site runs its own check on its own data. One site may use a newer list, or a different set of signals, than the next. A "not detected" result describes one check on one day.
Why is my temp mail detected?
A temp mail address is detected when its domain appears on a domain list of throwaway services. A temp mail detector may also flag it because its mail server, age or signup pattern matches a known disposable service.
Is there a temp mail that is never detected?
No provider of temp mail can promise that it is never detected. Lists keep growing, and sites can check again at any step. Treat any claim of undetectable temp mail with caution.
What does "temporary email services are not supported" mean?
The message means the site matched your address against a disposable list and refused it. The site wants a mailbox it can reach later. Enter an address you own and the form should accept it.
What does it mean when a temp mail is blacklisted?
A domain is blacklisted when it sits on a blocklist of disposable domains. Many sites rely on the same public lists, and a domain can appear on one list and not on another.
Can a real email address be flagged as disposable?
Yes, a genuine mailbox can be flagged as disposable. Privacy relays, forwarding domains and brand-new domains sometimes sit on lists or look suspicious to an age check. Ask the help desk to review it if it happens to a work address.
During implementation, use the free disposable email detection tool to spot-check addresses from real signup traffic. Those checks help confirm that your blocking policy catches risky domains without creating unnecessary friction for legitimate users.
Does BillionVerify offer temp mail?
BillionVerify does not sell temp mail or temporary inboxes. We offer a free disposable email check and a public domain list for developers. Our servers are in France (EU), and a data processing agreement is available.
When reviewing false positives or a sudden change in detection rate, recheck representative addresses with the disposable email checker. A repeatable manual check makes it easier to separate a rule problem from a genuinely new disposable provider.
How do I block disposable email on my website?
To block disposable email, check each address against a domain list when the form is submitted. Then explain the problem to the user or tag the signup as low trust. The open-source library and the hosted check both cover this step.
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