Email Verification: A Brief Introduction

Article author
Sarah Malone


Email Verification Graphic

Running a successful email campaign takes much more than a powerful message. You need to make sure you deliver the right message, to the right people, at the right time, and to the right email domain.

Email verification is an essential cog in the motion of any email engagement workflow. It is the process of validating the authenticity and accuracy of an email address before you send any messages to your ideal contacts.

There are many advantages to email verification, including:

  • Protect the health and reputation of your email domain
  • Increase your email delivery rates and ensure your message reaches the right people in the right inboxes
  • Identify stale data before you message contacts on outdated or invalid email addresses that can harm your domain reputation and decrease your engagement rates
  • Reduce the risk of being flagged as SPAM

Refer to the sections below for more information about how email verification tools work and what catch-all emails mean for your campaigns.

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Email Verification Tools

Many people use email verification tools such as ZeroBounce, Mailfloss, Neverbounce, or Hunter to help protect their domain reputation and increase the performance of their email campaigns. However, if you use a third-party email verification tool in conjunction with Apollo, it can often be counterproductive to the success of your sequences.

Every third-party email verification tool has developed its own process to verify your emails. This means that the effectiveness or reliability of email verification relies greatly on the specific process of the tool you choose. Most competent tools include steps such as:

  • A syntax check to ensure there are no typos or questionable characters in the email address
  • A domain check to verify the existence of the domain name on which the email is hosted
  • An email ping to check that the specific email address exists

Although these techniques can be effective, they can also greatly affect your coverage. For example, if an email service is temporarily unreachable when the verification tool checks its domain, you exclude all the emails from an organization in one swift check.

Furthermore, the majority of popular email verification tools use a method called SMTP tickling.

Hold the Phone, What's that?

Simple Mail Transfer Protocol (SMTP) is a Transmission Control Protocol/Internet Protocol (TCP/IP) for sending messages. Most email verification tools leverage SMTP tickling to ask an email service if an email exists, thereby verifying its validity before you send any messages to it.

SMTP tickling does not differentiate between valid and invalid "catch-all emails". Therefore, this method does not confirm if the email address will link you to the right person, or if your messages will be auto-dumped into a default inbox that no one will see.

It's Not All Doom and Gloom

Although catch-all domains can still lead you to the right person; when you use third-party verification tools, is it very difficult to guarantee that they will. Hop into the Email Verification: The Apollo Process article to learn more about how Apollo's robust, built-in email verification process helps you to overcome this issue.

Finally, it's important to note that a third-party tool is not an all-encompassing solution. Several factors impact your bounce rate, some of which email verification tools cannot help you with. For more information, refer to the "Email Accuracy" section of the "Email Verification: The Apollo Process" article.

Read on to find out more about what catch-all emails are and why they matter.

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Catch-All Emails

Catch-all emails are the email addresses that belong to a catch-all mail server. This means that if you send an email to any address that belongs to a specific domain name—even if the address does not exist, or is written incorrectly—the catch-all mail server accepts your email.

It's Polyonymous!

You may have heard of the terms "accept-all emails" or "wildcard email aliases" too. Fear not, observant souls—catch-all emails go by many names but the same definition applies to them all.

Here's an example of how catch-all emails can be problematic for your campaigns:

Domain Name Existing Email Addresses from Example Domain Catch-All Inbox Invalid Email Address,,,

You have an email for Terry at Example. His email is However, Terry stopped working at Example 1 month ago and the company is yet to replace him. Example has 4 existing employee email addresses, plus 1 catch-all email address. This means that even though Terry left the company and his email address is no longer valid, the message you send to will land in the catch-all inbox.

Catch-all email servers exist so that important emails still reach a company inbox, despite sender errors. For this reason, a large number of companies have a catch-all email server. However, with the rise in spammers taking advantage of catch-all email domains, only some companies still dedicate resources to keep on top of reviewing the emails in their catch-all inboxes.

In short, if no one checks this catch-all inbox regularly, chances are the emails that land there won't be seen by anyone, let alone opened or read by the specific person you are trying to reach.

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Apollo-Verified Emails

Email Verified on Search Page

Third-party email verification tools sometimes flag Apollo-verified emails as invalid. This is because most tools cannot distinguish between valid and invalid catch-all emails.

Many of the business emails from contacts that you prospect in Apollo could have a catch-all domain. This means that when you rely on third-party email verification tools—unless you are willing to invest hours and hours manually verifying which catch-all emails are valid—you will most likely rule out all catch-all emails from your lists. When you do so, you risk losing a big chunk of the potentially qualified company domains in your pipeline.

However, there is a much easier, more accurate alternative. Apollo already includes a built-in email verification process with a 91% email accuracy rate that can differentiate between valid and invalid catch-all emails. This means that you do not need to use a third-party verification tool alongside Apollo. Instead, when you rely upon Apollo's verified emails you know that you automatically include the valid catch-all domains in your sequences and exclude the invalid ones. As a result, you are better equipped to reach more of your ideal contacts without putting your domain reputation at risk.

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Next Steps

Next Steps Graphic

Now that you have learned more about email verification tools and catch-all emails, jump into the Email Verification: The Apollo Process article to find out more about Apollo's verification process, why it is different, and what it means for the success of your email campaigns.

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