Why top brands use real-time email validation—and you should too!

Amy Elliott Amy Elliott
· 10 min read · Tips and resources · November 15th, 2022
Real-time email validation preemptively keeps your email list healthy so you can focus more on sending and less on cleaning up! Here’s how it works and how to get started.

Keeping your email recipient list clean and free from invalid emails is crucial if you want to maintain a good sender reputation and a high level of deliverability. Periodically checking your list with an email verification tool is great! But what if you could take your list maintenance to the next level?

With real-time email validation, you can!

Real-time email verification lets you stop invalid emails in their tracks, making managing your recipients easier and providing a better user experience. 

In this article, we’ll share how real-time email validation works, why you should be using it, and how you can easily set it up with MailerSend. Let’s go!

What is real-time email validation?

If you’re following email sending best practices, you’ll already know that email validation involves running your email list through a verification tool in order to identify invalid emails that should be removed.

We won’t go through all the ins and outs of email verification here, but if you’d like to learn more, head over to this article all about email verification and how it can optimize your transactional email.

Real-time email verification does just that, but uses an API integrated into your webforms to run checks against email addresses as they are being entered. This allows you to catch them before they get anywhere near your email list. Pretty cool, right?

How real-time email verification works

Using a simple email validation API, any developer can integrate real-time email validation with your website or app. When an email address is entered, the email validation service you are using verifies the validity of the email. 

The email validation checker will then return the status of the email address in real-time so that your website or app can decide what to do based on whether the email is valid or not. 

For example, if the email address is invalid, you can instruct your website or app to display an error message to the user, prompting them to enter a valid email address.

Graphic showing the process of real-time email validation.

Other email validation methods

In addition to preventing invalid emails with real-time verification, it’s also recommended that you periodically perform manual email list cleaning as well. (No, we don’t mean picking out emails by hand, one by one! An email verifier will do this for you.)

The reason for this is that, even if an email address is valid when a user signs up, it doesn’t mean their email address will remain active forever. So it’s important to run a check around every 6 months to clean up any emails that have gone inactive in that time. 

A manual email validation check involves uploading your list via CSV to an email validation tool, like MailerSend’s. Once you’ve uploaded your list, MailerSend will do its magic, validate your emails and return a detailed report about the status of each recipient. You can then download your report and easily add invalid and risky emails to your suppressions list.

Here’s all the errors MailerSend detects

MailerSend runs a fairly comprehensive set of checks—it’s even able to detect email addresses that have had past delivery issues. Here’s all the statuses that a MailerSend email verification report can return. 

Send to


Email is safe to send.



The recipient's mail server will accept emails to this address but we cannot guarantee this email address belongs to a person.

Mailbox full

The recipient’s inbox is full and may not be able to receive new emails.


Email is role-based and may not be associated with a single, specific person but a group of people.

Past delivery issues

We have detected past delivery issues while sending to this email address. 


We are unable to determine if the email is valid.

Do not send to

Syntax error

The email address is not valid.


The email address has a typo. Correct the email address and retest.

Mailbox not found

The recipient’s inbox does not exist.


This is a disposable email address that leads to a temporary inbox and should be removed from your lists.

Mailbox blocked

The email address’ mailbox is blocked by its service provider due to poor sending practices.

The benefits of real-time email validation

We’ve explained what real-time email validation is but, beyond keeping your email list clean, why should you use it? Here are 8 real advantages of real-time email verification. 

1. Maintain a healthy sender reputation and boost deliverability

Sender reputation is a scoring system used by Internet Service Providers (ISPs) to help combat spam. It works by assigning a high (good) or low (bad) score to senders based on their sending practices. 

If you keep a healthy, clean email list, you’ll reduce email bounces, spam complaints and unsubscribes. This will signal to ISPs that you’re a good sender, thus helping you to improve and maintain a good sender reputation. 

A healthy sender reputation helps boost your deliverability. Higher deliverability rates help you maintain a healthy sender reputation. And that’s the cycle of email deliverability. 

When it comes to maintaining and improving your sender reputation, cleaning your email list is essential. Adding in real-time email verification will make looking after your email list even easier, keeping your list cleaner between manual checks.

2. Reduce the risk of blocklisting

The cleaner your email list, the more real, engaged recipients you have. A high number of spam complaints, spam traps and other invalid email addresses that result in high hard bounce rates are issues that can result in your IP address or domain being blocklisted. They tell ISPs that you are not maintaining your email list. 

With real-time validation, invalid emails are caught before they ever get near your list, so the risk of being blocklisted is greatly reduced. 

3. Increase engagement

Engagement metrics such as clicks, forwards and open rates help ISPs to determine if you’re following best practices for your content and email list. Low engagement signals that either your recipients aren’t interested in your messages or that your email list is full of bad emails that don’t actually belong to real people. On the other hand, high engagement rates show that you’re sending your emails to a valid list of recipients who want to hear what you have to say.  

Keeping a clean email list will help you to avoid the spam folder, deliver more emails and increase engagement.

4. Increase conversions

The cleaner your email list, the higher your deliverability and the more real recipients you’ll be able to reach. Combine this with more people engaging with your content and conversion rates will increase. 

5. Enjoy more accurate data

Email engagement metrics are important for helping you to optimize your emails and sending strategy, but not if they’re inaccurate. Keeping your email list clean with real-time verification will allow you to make use of more accurate data.

Invalid emails skew data by making your engagement metrics appear much lower than they really are. For example, if you send an email to 100 people and 50 people click, your click rate will be 50%. But, if in fact 25 out of those 100 recipients are invalid, that means your total number of recipients is actually 75, not 100. So your click rate would be 66%. Results that you may put down to bad content or design might actually be because of invalid emails.

6. Improve the user experience

Imagine you sign up for a service or product only to never receive any email from them. It could be that you simply entered your email address incorrectly, but you’d never know if the website or app doesn’t inform you. 

Real-time email validation solves this issue by immediately displaying an error message to the user if they enter an invalid email address. All they need to do is enter it again correctly and they’re good to go. 

7. Save on sending costs

If improving your sender reputation, deliverability and engagement wasn’t enough, how about saving money? 

If you’re sending emails to a bunch of people that don’t actually exist, you’ll still have to pay for those sendings. Having a significant number of invalid email addresses will drive your sending quota up to much more than you need, resulting in unnecessarily higher sending costs. 

Making sure those invalid emails never hit your list means your recipients will stay as valid as possible and you’ll never pay more than you need to for your sendings. 

8. Avoid legal ramifications and fines

There are regulations in place, such as CAN-SPAM, that protect consumers from spam, and violating them can land you a hefty fine. Invalid emails that lead to spam traps are just waiting to catch out senders who aren’t following best practices, so it’s better to be safe than sorry and keep your list clean.

Top brands that use real-time email validation

More and more top brands are implementing real-time email verification on their apps or websites. That’s because it’s the most efficient way to consistently maintain a healthy email list. Let’s take a look at a few examples. 

1. Glovo

Food delivery app Glovo has a presence throughout Europe, Central Asia and Africa. They display the following error when you try to sign up with an invalid email. 

Example of real-time email validation used by Glovo.

2. Apple

Apple is one of the most recognizable brands on the planet, and there’s no way you’re getting past their sign-up page with an invalid email address thanks to real-time verification. 

Apple's real-time email validation.

3. Slack

Everybody’s favorite communication and collaboration tool also uses real-time email validation, displaying a simple message: email check failed. 

Slack's real-time email verification message.

4. GitHub

Open source community GitHub goes a step further by notifying the user that the email is invalid and making a suggestion to correct the typo. 

Github's real-time email verification message and suggestion.

5. MailerSend

We wouldn’t be touting the benefits of real-time email verification without using it ourselves!

MailerSend real-time email verification invalid email message.

How to set up a real-time email verification API with MailerSend

1. If you haven’t done so already, create an API token so that you can link your app and MailerSend with the API key, by going to Settings, API tokens and clicking Generate token.

2. Configure your app or website so that the email address will be sent to MailerSend for verification when the user submits it. When this happens, your app should perform an API call with the following POST request to verify a single email:


The request body should look like this:

    "email": ""

You should then return the status before the email address is added to the database. Here’s an example of a response:

    "status": "valid"

Say goodbye to invalid emails

Real-time email address verification is the most efficient way to keep your email recipient list clean and healthy. It will help improve deliverability and engagement and make your periodic, manual clean-ups less of a chore by preventing invalid emails from building up in between checks. Kind of like using a Roomba between deep cleans of your house. 

With MailerSend’s email validation service and super simple API, and a few tweaks to your website or app, you can quickly set up real-time email validation and let MailerSend do the rest!

Do you have any other tips for avoiding invalid emails getting onto your email list? Let us know in the comments!

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Amy Elliott
I’m Amy, Content Writer at MailerSend. As a child, I dreamt about writing a book and practiced by tearing pages from an A4 notepad and binding them with sugar paper. The book is pending but in the meantime, I love taking a deep dive into technical topics and sharing insights on email metrics and deliverability.