Temp Mail With a Custom Username: Rules, Domains and Taken Names
Set a custom username for temp mail in the free TempMailFast app: which names are allowed, what to do when one is taken, and what happens when you change it.
You can get temp mail with a custom username in the TempMailFast app for iPhone and Android, in both the free and premium modes. Use letters and numbers only, and choose a domain from the list. The website always gives you a random username, so use the app when the name matters.
The longer answer
A custom username is the part before the @. You're still getting a normal TempMailFast address: it only receives email, and on the free app it lasts 20 minutes.
Setting a username (or switching domain) creates a brand-new address with its own fresh time. Your previous inbox is lost, so set the name first and request any codes after.
Each full address can only be created once. If someone (including you, last week) already created that username on that domain, the app won't let you take it again, even if the old address has expired. The same name may still be free on a different domain.
How to set a custom username in the app
- Install the app from the App Store or Google Play.
- Open it. The app creates a random address straight away. If you're happy with a random one, skip to step 4.
- Set your username and pick a domain. Enter the part before the @ (letters and numbers only) and choose a domain from the free list. Premium adds premium domains to the list.
- Copy the address with the copy button and paste it into the sign-up form. Copying avoids the one-letter typo that sends your code somewhere else.
- Go back to the app to read the email. There are no push notifications, so switch back and check the inbox while you wait.
- Finish within 20 minutes on the free mode. Once the address expires, it and its mail can't be recovered.
New to temp mail? The getting started guide covers the website first.
Username rules at a glance
| Rule | What it means for you |
|---|---|
| Letters and numbers only | Dots, dashes, underscores and other symbols can't be typed. "couponoct" works, "coupon.oct" doesn't |
| Not case-sensitive | "CouponOct" is saved as "couponoct", so capitals make no difference |
| Used once, can't be reused | A username that was used before on that domain stays taken, even after it expires |
| A taken name may be free on another domain | Try the same name on another domain from the list (it may or may not be free) |
| Changing the name or domain starts over | Do it before you request a code, not after |
Picking a name that doesn't give you away
Whatever you type gets stored by the site you sign up to, next to anything else you hand over, so skip anything you'd mind a stranger reading.
- Good: a label for the job, like "pizzacoupon" or "webinar2026". Easy to read out or type on another device, and it says nothing about you.
- Fine: the random string the app created, when you'll only ever paste it.
- Avoid: your real name, your name plus a birth year, or a handle you use on other sites. Anyone searching that handle can link the throwaway sign-up to your other accounts.
Short, common names are more likely to clash with an address someone already created, so adding a couple of digits helps.
A memorable name doesn't expose your mail, though. App inboxes are private to the device that created them, so someone who knows or guesses the address can't open it. More on what can tie an address back to you in Can temp mail be traced?.
What can go wrong (and the fix)
| Problem | Likely cause | Fix |
|---|---|---|
| "The username already exists. Please choose a different username." | Someone used that name on that domain before | Add digits, pick another name, or try the same name on a different domain |
| You can't type a dot or hyphen | Only letters and numbers are allowed | Run the words together, like "pizzacoupon" |
| The verification email vanished | You changed the username or domain after asking for the code | Settle on the final address, then request a new code |
| The site says the email isn't allowed | The site blocks that domain. The username usually isn't the issue | Try another domain (the same name may or may not be free there). If every domain fails, read why sites block disposable email |
| The code arrives after the address expired | Free addresses last 20 minutes | Request a fresh code on a new address, or use premium for slow senders |
Website or app: where you can choose the username
On tempmailfa.st, every address gets a random username. The New address button gives you another random one, possibly on a different domain, but you can't type the name or pick the domain.
In the free app you get both, with the same 20-minute limit. Premium keeps custom usernames and adds more domains and longer-lasting addresses (app guide).
A memorable username doesn't make it a keeper, though: the address still can't send or reply, and it's the wrong choice for banking, work or anything you'll need to recover later.
Frequently Asked Questions
Can I choose my own username on the TempMailFast website?
No. The website always creates a random username. Custom usernames are an app feature, in both the free and premium modes.
Why does the app say my username already exists?
Each full address can only be created once, and that one was used before, even if it has since expired. Add a few digits or try the same name on another domain.
Can I use dots or underscores in a custom username?
No. Usernames are letters and numbers only, so run words together instead, like "pizzacoupon".
Do capital letters matter in a custom temp mail address?
No. Addresses are saved in lowercase, so "PizzaCoupon" and "pizzacoupon" are the same address. Capitals you type are simply ignored.
