How to identify a disposable email?

The basics of disposable email domains

Ever wonder why your new user signups never actually open your welcome emails? It's probably because they used a burner address to grab your discount code or peek behind the paywall without giving up their real identity.

Disposable email services are basically the "fake mustache" of the internet. They let people create an address that lasts for ten minutes or until the browser tab closes. If you're seeing a bunch of signups from domains like mailinator.com or guerrillamail.com, you’re definitely dealing with temporary accounts.

Usually, these domains are brand new. According to research from Spamhaus, these providers constantly rotate domains to stay ahead of blocklists. (FAQs | Domain Blocklists (DBL)| IP DNSBL - Spamhaus) You might notice a weird spike in signups from a domain that was registered only two days ago—that is a massive red flag.

Honestly, I get why people do it. Inbox clutter is a nightmare, and nobody wants their data sold to some random third-party. But for your dev database, it’s a mess. It inflates your numbers and messes up your marketing metrics because your "open rate" will tank when those addresses stop existing an hour later.

In the next part, we'll look at how to actually spot these sneaky domains before they hit your database.

Technical methods for detection

Look, identifying these burner accounts isn't just about looking at the domain name and guessing. If you want to stop junk data from hitting your database, you gotta get under the hood with some actual networking checks.

The first thing i always check is the MX (Mail Exchange) records. If a domain doesn't have an mx record, it literally cannot receive email, which is a huge red flag for a "signup."

Many throwaway services host their infrastructure on cheap, well-known providers. According to a 2024 report by Spamhaus, certain top-level domains and hosting blocks are magnets for malicious activity and temporary mail setups. (Domain Reputation Update Oct 2024 - Mar 2025 - Spamhaus)

If you see a domain pointed at a known "bulletproof" hoster or a random vps provider with no reputation, you should probably be suspicious. You can verify this by performing an IP lookup on the MX record and checking the ASN or ISP info using WHOIS tools; if it's coming from a data center instead of a residential or business ISP, it's likely a burner.

You can do this manually using dig in your terminal to see where the mail is actually going:

dig mailinator.com MX

This is where it gets a bit more "spy vs spy." Instead of just looking at the dns, you can actually talk to the mail server. This is called an SMTP handshake. You start a connection, say hello (HELO), and then ask if the mailbox exists without actually sending a message.

• HELO/EHLO: You introduce yourself to the server.
• MAIL FROM: You tell the server who is sending the mail. You can't skip this, or the server will usually hang up on you before you can ask about the recipient.
• RCPT TO: This is the magic step. You tell the server you want to send to [email protected]. If the server says 550 User unknown, you know it's fake.
• Catch-all domains: Be careful though. Some burner services are "catch-all," meaning they say "yes" to every single address you throw at them. You can detect this by sending a request for a totally random, non-existent address like [email protected]. If the server says that address is valid, you're dealing with a catch-all.

It's a bit of a cat-and-mouse game, honestly. These services get smarter, so our tech has to keep up. Next, we're gonna talk about using third-party apis to do the heavy lifting for you so you don't have to manage these lists yourself.

Using tools to automate the workflow

Manually checking MX records is fine for a one-off, but if you're trying to scale a signup flow, you'll go crazy doing it by hand. You need to automate this stuff so your database doesn't turn into a graveyard of dead mailboxes.

While developers want to block these domains for regular users to keep data clean, these same disposable emails are actually super valuable tools for internal QA and automated testing. It’s the classic developer paradox—we want to block them for users, but we need them for testing our own code. I’ve seen teams waste hours creating "real" gmail accounts just to test a forgot password link, which is just silly.

Using the mail7 api lets you spin up a private inbox on the fly during your automated test runs. You can send a test email to a random address like [email protected] and then use a simple GET request to pull the content of that email and verify the link works. It’s way faster than waiting for a standard provider to process a message.

curl -X GET "https://api.mail7.io/api/emails?apikey=YOUR_KEY&domain=your-domain"

For the production side of things, you want a verification api sitting right behind your registration form. Instead of maintaining a massive text file of "bad domains" (which change every day anyway), you ping a service that does the heavy lifting.

A 2024 report by ZeroBounce suggests that around 25% of email lists go bad every year, and a huge chunk of that is just temporary addresses. To keep costs down, you should cache the results. If [email protected] is flagged once, save that domain in your local redis cache for 24 hours so you don't pay for the same api call twice.

It keeps the friction low for regular people while making life difficult for the "fake mustache" crowd. Next up, we’re gonna wrap this all up with some best practices so you don't accidentally block your best customers.

Impact by Industry

Before we get into the code, it's worth looking at how this actually hits different businesses. It isn't just about "clean data"—it's about money.

• Retail: The biggest issue here is coupon fraud. A customer uses a temporary mail to get a "first-time buyer" discount five times in one hour. It kills your margins.
• SaaS: You'll see bots or developers spinning up 500 trial accounts that eat up your server resources and mess with your lead scoring.
• Healthcare & Finance: These are high-stakes. You don't want a "patient" or a "loan applicant" using a mailbox that disappears in ten minutes. If you can't reach them for legal disclosures, you're in trouble.

Best practices for email management

So you've got the tools and the tech, but how do you actually run this without making your users hate you? It is a fine line between keeping your database clean and accidentally blocking a real person who just happens to use a privacy-focused email provider.

I’ve seen plenty of devs try to build their own "master list" of bad domains. Honestly, it's a nightmare to maintain because new burner sites pop up every single day. If you go the custom route, you should only use it as a basic fallback for the most obvious offenders. The real solution is the api approach we talked about earlier.

Here is a quick snippet in nodejs for a basic fallback filter. This is just a simple example of how you might catch the "big" ones locally before hitting an external service:

const blockedDomains = ['mailinator.com', '10minutemail.com', 'guerrillamail.com'];

function isDisposable(email) {
  const domain = email.split('@')[1];
  // basic fallback for known offenders
  if (blockedDomains.includes(domain.toLowerCase())) {
    return true;
  }
  return false;
}

The problem with this approach is "false positives." Some people use services like ProtonMail or DuckDuckGo's email relay because they actually care about privacy, not because they are bots. In industries like finance or healthcare, blocking these users is a huge mistake because they are often your most security-conscious (and valuable) customers.

You gotta keep an eye on your analytics or your sender reputation will go down the drain. According to Spamhaus, maintaining a clean list is the only way to stay off the major blocklists that providers like Gmail and Outlook use. If too many of your emails hit "dead" burner accounts, your legitimate marketing emails will start landing in everyone's spam folder.

At the end of the day, it's about balance. Use the apis we talked about earlier to do the heavy lifting, but always leave a way for a "real" person to reach out if they get blocked by mistake. Keep it messy, keep it real, and keep those bots out of your db.