Why Websites Block Disposable Email: We Analyzed 5 Blocklists

Why We Ran the Numbers Ourselves

If you have ever pasted a temporary email address into a signup form and been told to "please use a permanent email address," you have met a disposable-domain blocklist. As the operators of a disposable email service, we wanted to know exactly what sits behind those rejections. So in July 2026 we downloaded the five most widely used public blocklists from GitHub, normalized them, counted them, and compared them domain by domain. Every number in this article comes from that analysis, which we ran on July 17, 2026 — nothing here is quoted from someone else's blog post.

First, the motive. Websites block disposable addresses for practical reasons: fake accounts inflate user counts and pollute analytics, free-trial abusers cycle through fresh inboxes to reset limits, marketers hate sending campaigns to inboxes that self-destruct within the hour, and fraud teams treat an unreachable user as a risk signal. None of this requires malice on your part. But from the website's side of the form, an address that stops existing in sixty minutes can look indistinguishable from abuse infrastructure — so many sites simply block the whole category.

The Five Blocklists Almost Everyone Uses

Nearly every "disposable email detected" message traces back to a handful of open-source GitHub repositories. The most cited is disposable-email-domains, a hand-curated list where every addition arrives as a pull request with screenshot evidence — PyPI, the Python package index, uses it in production. The disposable/disposable project takes the opposite approach: a crawler that aggregates dozens of sources and regenerates its list every 24 hours. Mailchecker ships its list inside a validation library available in more than eight programming languages. Fakefilter runs automated monitoring of known temp-mail providers and publishes fresh data daily. And ivolo/disposable-email-domains, once a standard choice, now carries an official notice that it is no longer maintained.

Our method was deliberately boring. We fetched each repository's raw list file, lowercased every entry, stripped comments and blank lines, removed duplicates, and compared the resulting sets with standard Unix tools. The same normalization was applied to every list, so the counts below are directly comparable.

How Big Is Each List?

Here is what we measured on July 17, 2026, after normalization. The spread surprised us: the smallest active list is roughly one twenty-fifth the size of the largest list.

The sizes are really philosophy statements. Fakefilter keeps only domains it can verify are working right now, so it stays small and current. The aggregator swallows everything its sources publish, so it grows large. And ivolo is the biggest precisely because nobody is removing dead entries anymore — size, on its own, tells you nothing about quality.

The Surprise: The Lists Barely Agree

Merging all five lists produced 162,327 unique domains. Then we computed the intersection — domains that appear on every one of the five lists — and got 236. That is about 0.15 percent. Even after dropping the unmaintained ivolo list and keeping only the four actively maintained ones, the picture barely improved: 75,497 unique domains combined, of which just 329 appear on all four.

The pairwise numbers explain how that happens. Mailchecker and fakefilter, both actively maintained, share only 482 domains — about 10 percent of fakefilter and under 1 percent of mailchecker. The curated disposable-email-domains list overlaps mailchecker on just 47.2 percent of its entries. The one place we found near-total agreement is by construction: the 24-hour aggregator contains 95.5 percent of the curated list and 99.9 percent of fakefilter, because it ingests both of them as sources.

Why so little consensus? Each project answers a different question. Evidence-based curation asks "can a human prove this domain serves disposable inboxes?" Automated monitoring asks "is this domain working right now?" Aggregation asks "has anyone, anywhere, ever flagged this domain?" Add in the fact that temp-mail services rotate domains constantly, and any snapshot starts aging the moment it is published.

How Websites Actually Check Your Address

The simplest and most common implementation is an exact domain match at signup: the site splits your address at the @ sign and looks the domain up in a vendored copy of one of these lists, often installed as an npm or pip package. It is fast, free, and requires no network call — but it is only as good as the list's last update, and as we just measured, which list you pick changes the outcome dramatically.

More sophisticated sites go beyond static lists. Because disposable providers often share mail infrastructure, resolving a domain's MX records and comparing the mail hosts against infrastructure already linked to known disposable services can catch a brand-new domain before it appears on any list. At the top of the stack sit commercial verification APIs such as ZeroBounce, Kickbox, and Abstract, which layer blocklists, MX and DNS analysis, SMTP-level probing, and pattern detection trained across millions of verifications. These services catch new domains faster than any single public list — at the cost of a paid API call per signup.

Why One Site Accepts an Address Another Rejects

Our overlap data explains a common user experience: the same temporary address sails through one signup form and bounces off another. With only 0.15 percent of domains agreed on by all five lists, the choice of list — and how recently the site refreshed its copy — effectively decides your fate. A domain added to fakefilter today may take a day to propagate into the aggregator and may never meet the evidence bar of the curated list.

Staleness cuts both ways, too. A site still bundling the deprecated ivolo list is checking against 121,569 domains, many of them long dead, while missing every disposable domain created since the project's last meaningful update in March 2025. That site will reject addresses no one has been able to create for years and happily accept this month's newest temp-mail domains.

What to Do When Your Disposable Address Is Rejected

If a signup form rejects your temporary address, the fix is usually one click away: generate a new address on a different domain. Blocklists match domains, not services, and no list we measured comes close to covering all of them — remember, the four active lists collectively know 75,497 domains but agree on only 329. Providers that offer multiple domains give you room to retry immediately.

Match the tool to the relationship. For one-time downloads, trials you will not keep, and newsletter shields, a disposable address remains the right instrument, and a rejection just means trying another domain. For accounts you actually intend to keep — anything involving payments, recovery, or long-term access — use a mailbox you control, or an alias on your real account, so a future password reset does not land in an inbox that no longer exists.

Blocklists are blunt instruments. Our measurements show they disagree far more than they agree, go stale quickly, and encode very different definitions of "disposable." Knowing that takes the mystery out of the occasional rejection: it is not a judgment about you, just an artifact of whichever text file a developer downloaded, on whatever day they downloaded it.

If you want to inspect the raw data yourself, start with the most widely deployed curated list — the same one PyPI uses to screen registrations. disposable-email-domains on GitHub↗

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