If a site rejects your temp mail address, it has recognised the domain as disposable and decided not to accept it. That's the site's call, and the fix is an address it will take: an alias that forwards to your real inbox, or your real address. If the form accepted the address but the code never came, that's a different problem with different fixes. Both are covered below.
Two problems that look alike
People say "temp mail doesn't work" about two quite different things. Work out which one you have first.
| What you see | What's going on | What to do |
|---|---|---|
| "Please use a valid email" | The site blocks the domain | Use an alias or real address |
| Form accepts it, no email comes | The sender is slow or won't send | Wait, resend once, then alias |
| Account made, then limited | The site flagged the new account | Add a contact method you keep |
The first is a decision the site has made. The second is usually about delivery. The third is the site deciding later, after it has seen how the account behaves.
How sites spot a disposable domain
The check looks at the part after the @. The name in front doesn't matter, so changing it won't change the result. The common methods are:
- Public blocklists. There are open-source lists of disposable email domains on GitHub with thousands of entries. Signup forms and code libraries can check against them in a single line.
- Email validation services. Paid services that look up an address and label it as valid, risky or disposable. Bigger sites often use one.
- Mail server checks. Every domain publishes records saying which servers handle its mail. Many temp domains share the same servers, so one known server gives away a whole group of domains.
- Risk signals. Brand-new domains, or domains appearing in lots of signups in a short time, get treated as risky.
Not every site blocks at the door. Some let you in, then slow the account down, limit what it can do, or ask for a phone number later. To see whether a domain is on the biggest public list, try our disposable email checker.
Why popular temp domains get listed fast
Free temp mail works by sharing a small number of domains between a lot of people. A busy domain turns up in a huge number of signups, someone notices, and it gets added to the lists. The more popular the service, the faster that happens. That includes the domains this site gets from mail.tm.
New domains appear and get listed in turn. So no free temp mail stays "undetectable" for long, whatever a service's marketing says. If a site checks, it will usually catch a well-known temp domain. That's by design, and it's not something to work around.
Why sites do it
Blocking throwaway addresses isn't about annoying you. The usual reasons:
- Fake accounts and spam. Disposable addresses make it cheap to create lots of accounts.
- Free trial abuse. One person claiming the same trial or new-customer discount over and over.
- Bounces. Mail to addresses that vanish bounces, and lots of bounces push a sender's mail into spam for everyone.
- They need to reach you. Password resets, receipts and security alerts only work if the address still exists next month.
People with good reasons get caught in the same net, which is frustrating. It's still the site's rule to set.
What to do when the form rejects you
Don't cycle through other throwaway domains. The site has told you it wants an address that lasts, so give it one that still protects your main inbox.
- Use an alias. Firefox Relay, DuckDuckGo Email Protection, Apple's Hide My Email, SimpleLogin and addy.io all give you an address that forwards to your real inbox. The site never sees your main address, and you can switch the alias off if the spam starts. See email alias vs temp mail for how they differ.
- Use your real address if you'll keep the account and trust the site.
- Use plus addressing where it's accepted. yourname+site@gmail.com lands in your normal Gmail inbox. Outlook.com often accepts it too, but doesn't promise to. It's good for filtering and spotting who sold your address, but it isn't private: your real address is in plain sight. If a form rejects the plus sign, use an alias instead.
If a site refuses temp mail, treat it as a sign you'll need to hear from them again. That's a job for an address you keep.
For anything with a free trial and card details, use an address you keep anyway, so you see the "your trial is ending" email before you're charged. There's more on that in is temp mail safe and legal.
What to do when the code doesn't arrive
If the form took the address but nothing has shown up, work through this in order:
- Wait a minute. Some senders queue mail and send it a little later. On this site the inbox checks for new mail every 5 seconds, so there's no need to reload, and reloading would give you a new address.
- Check it's the same address. If you pressed New address or closed the tab, the old inbox is gone. Use the Copy button rather than typing, so there's no typo.
- Check the spam folder if you used an alias or your real inbox. Codes sometimes land in spam or a promotions tab. A temp inbox shows everything in one list, so just look for a sender name you didn't expect.
- Resend once. Pressing resend over and over can trigger the site's rate limits and lock you out for a while.
- Try one fresh address. If that doesn't work either, the sender probably won't deliver to temp domains.
- Switch to an alias. At that point it's the quickest way to get the code.
Why some codes never arrive
Some senders, and the email platforms they use, refuse or delay mail to known disposable domains. They do it to protect their delivery reputation, and nothing on the receiving side can change that. Sometimes the temp mail provider itself is busy or briefly down, which is why this site falls back to a backup provider when mail.tm isn't responding. Either way, if two tries have failed, stop retrying and use an address the sender will deliver to.
Where temp mail still works well
Plenty of sites don't check at all, and temp mail is still the right tool for:
- A one-off download or a whitepaper behind an email form
- Reading a newsletter once to see if it's worth it
- Checking out a site before you trust it with your real address
- Testing your own signup emails (see temp mail for developers and QA)
For those, a free temp inbox does the job in seconds. If you want to compare options, the 20 temp mail and alias services compared guide groups them by type. For signing up to Instagram, Discord and the rest, see temp mail for social media signups.