Why sites want to stop these addresses
A lot of websites hate free throwaway inboxes. They want real users who might pay or come back. A short-lived address lets one person make many accounts, skip a paywall, or grab a free trial again and again. So sites try to spot and reject these addresses at sign-up. Our page on why sites block temp mail covers the money side in more depth.
To block an address, a site first needs a way to know it is throwaway. That is where lists come in.
Public block lists everyone shares
The most common trick is a shared list. Volunteers and companies gather the domains of known burner services and post them online for free. A developer downloads the file, loads the thousands of names into their site, and checks each new sign-up against it.
How a name lands on a list
A domain gets added when enough people report it or when a bot finds it hosting a public inbox. Once one big list adds a name, dozens of other lists copy it within days. That is why an old, famous service is blocked almost everywhere, while a newer address maker often gets through untouched.
Live checks on the mail server
Lists go stale fast, so stricter sites add a second step. They look at the mail server behind your address in real time. A few common probes:
| Check | What it asks | Weak spot |
|---|---|---|
| MX record | Does this domain even accept mail? | Real services pass it fine |
| Catch-all test | Does it accept any random name? | Some real hosts do too |
| Domain age | Was this name just registered? | Old burner domains pass |
| Pattern match | Does the name look random? | Easy to make names look normal |
These checks catch more addresses than a plain list, but they also flag some real people by mistake. That trade-off is why many sites keep their rules loose.
The endless cat-and-mouse game
Here is the loop that never really ends:
- A service starts up with a brand-new domain that no list knows.
- People use it, so it slowly gets noticed and reported.
- Block lists add the name, and sites start rejecting it.
- The service adds fresh backup domains, and the loop starts over.
Because of this loop, no block list is ever complete. There is always a gap between a new name going live and a list catching up. A good throwaway service keeps a pile of spare domains ready, so when one gets blocked, it simply hands you another. This is one reason a disposable inbox still works on most sites even after years of blocking efforts.
When a block gets it wrong
Block lists are not perfect. Sometimes they tag a normal small mail host as throwaway and lock out real users. Other times a fresh burner domain looks totally clean and sails right in. The people who run these lists cannot check every domain by hand, so mistakes in both directions are common. If a site ever rejects your good address by accident, it is likely a list error, not a rule about you.
If dodging junk is your real goal, you may not even need to fight a block. Our guide to stopping sign-up spam shows softer ways to keep your main inbox clean.
Staying a step ahead of the lists
Now you can see the full picture. Websites build lists to block disposable domains by pulling from shared databases and, sometimes, by testing your mail server live. But every list has a gap, and every live check can be fooled or can fool itself. A service that rotates in new names faster than the lists can catch them will keep working. So the "war" on throwaway inboxes is less a wall and more a race that neither side ever fully wins. For a wider look at your options, see our roundup of top services.