email validation glossary

Email Validation Glossary: The Terms You Want to Know

We’ve talked countless times about email validation and why it is so important. For email marketers and anyone doing any kind of business online, its benefits are indisputable. Today, we’ll do our best to define some of the most common terms related to email validation. So, if the terminology ever confuses you, this resource is always going to be here to help you out.

Email validation glossary: let’s start!

Abuse emails

This term refers to email addresses that belong to known email complainers, meaning people who have a history of marking emails as Spam. They’re risky, so ZeroBounce will always isolate them in your reports. However, that doesn’t mean you can’t send to them. It’s your decision.

Application Programming Interface (API)

An API works like a bridge that connects two applications, allowing one to extract information from the other and deliver it to you. It’s a piece of software that acts like an intermediary. The API calls the other application, requests and retrieves specific data for you. ZeroBounce has an email validation API that verifies your subscribers in real time.


It’s the most dreaded list to be on, if you’re an email marketer. Blacklists block domains, IPs or email addresses they distrust, which results in a hard bounce. A messy email list can get you on the blacklist, meaning that none of your emails will reach your subscribers’ inboxes. As an email sender, once you’re on the blacklist, you are persona non grata for Internet Service Providers (ISPs) and Email Service Providers (ESPs).

Bounce rate

It is the rate at which an email you send bounces or can’t be delivered. If you have a high bounce rate, it’s a sign that your email list is messy and needs to be cleaned. You can use an email validation service to get rid of invalid, dormant and fake email addresses.

Catch-all emails

This type of addresses are mailboxes on a domain that will “catch” all the emails sent to that domain, even if the address doesn’t exist. Usually, businesses and government organizations configure catch-all’s so they don’t miss any emails that may be trying to reach their domain.


An email is deliverable when the address you send to has a valid format and an MX record.


These are also known as temporary email addresses, that expire after a certain period of time. As you may have already guessed, people use them for short-term purposes: to register on forums, post comments on a platform or download a freebie.

Email deliverability

It reflects how many of your emails are delivered to the inbox. It is a crucial metric in email marketing, because it directly impacts your open and click-through rate. Have you read our Guide on email deliverability?

Email validation

It is the process that checks whether an email address exists and follows the correct format.

Email verification

Email verification is a more complex process that checks whether an email address belongs to a genuine, active recipient.

When asked about the difference between validation an verification, American software engineer Barry W.Boehm gave this brilliant answer:

Validation: Are we building the right product?

Verification: Are we building the product right?

Email checker, email verifier, email validator

It is the system that performs email validation and email verification. You may also find it online under names such as email list cleaning service or email cleaning service.


It is an anti-spam method to protect email users against unwanted messages. The receiving mail server will temporarily reject any emails coming from an unfamiliar sender. It will also tell the sender to send the email again in a few minutes. Your mail server will try to send the email until the receiver either accepts or rejects it. Read about our anti greylisting technology here.

MX (Mail eXchanger) Record

It is a Domain Name System (DNS) record that plays a crucial role in the delivery of your emails. The MX record redirects any email to a designated mailhost, pointing towards the location where the email should be sent. Here is a more complex definition of the MX record.

Role based emails

These emails belong to a position or a group of people within an organization. You will easily recognize them, as their format is usually: sales@, info@, team@, or contact@.

Spam traps

Spam traps are abandoned and repurposed email addresses. Email Service Providers (ESPs) and blacklist providers turn these addresses into traps for spammers. They don’t belong to real people and their sole purpose is to lure in spam senders.

Toxic domain

A toxic domain is known for abuse, spam and bot-created emails. Our email experts recommend that you do not send emails to any of your valid addresses that have a “toxic” flag.

SMTP Bounce codes

SMTP stands for Simple Mail Transfer Protocol. These are codes that you receive from different mail servers indicating why they didn’t accept the emails you sent to them. They play an essential role in understanding why your emails bounced. Your email validation service representatives may ask you for these codes to determine the reason of your bounces.


To whitelist means to allow someone to enter a group of trusted individuals. In the case of email, it means that your domain, IP and email address follow email marketing best practices. Hence, your emails will find their way to the inbox.


Is there any other term you’d like to learn more about? Let us know and we’d be happy to explain!