How to Verify Email Addresses


22.5% of your contact database will decay every year according to research conducted by Marketing Sherpa

Like everything in life, even email addresses have a limited life-span. Contact database decay occurs when a contact’s email address expires and is unable to accept any more emails. This is common with business email addresses.

Here are a few reasons why this can happen:

  • People change jobs,
  • People get fired,
  • Business gets acquired,
  • Business goes bankrupt, …

BONUS TIP: HubSpot developed an amazing free tool to calculate what kind of churn you can expect for your database

Why having expired data is bad

Having expired data in your CRM is harmful for at least two reasons. 

Firstly, from a business POV, it gives the false impression that you have a valid point of contact for a prospective business. 

Secondly, every email communication with expired contact will result in either a soft or hard bounce. This occurs when a recipient’s mailbox is unable to receive your email.

High bounce rate is the ratio of bounced emails against total number of send emails – hurts your domain ranking. This further increases the chances of your subsequent emails not getting delivered.

Therefore, one of the priorities for a database marketer should be keeping deliverability rate as high as possible. I’d argue that it’s a foundation of every successful email campaign.

Deliverability rate is the rate of emails successfully delivered to a person’s mailbox in relation to the total emails sent.

High bounce rate -> low deliverability rate -> lowers domain reputation

One of the best ways to fight this problem is to conduct:

Frequent email address verification.

Consider the following scenario.

You meet Amy on a tradeshow, the business talk goes well and she asks you to follow-up via email with more detail. She doesn’t have a business card with her since he left her bag at the booth but she tells you her email address. The following day you send an email and after a couple of seconds, you receive a message like the one below.

Notification received when sending an email to invalid email address

The email address is not valid, resulting in a hard bounce. Sending one such email won’t cause any harm to your domain. However, let’s say you’ve got 100 email addresses at the same tradeshow and 5 of them bounced – i.e 5% bounce rate? 

Now we are entering the danger zone. 

Doing this week in and week out with the same email addresses and your domain reputation might be ruined forever.

The aim is to identify invalid email addresses early-on and remove them from our contact list.

In a high-level view, each email address can be either valid or invalid. 

In reality, the spectrum between valid and invalid is rather wide and can take plenty of variants.

For instance, it’s possible to differentiate between a valid mailbox that is full and unable to receive an email temporarily – soft bounce – and a mailbox whose server is offline – hard bounce.

Some outcomes were common enough that status codes were developed to categorize them. Naturally, numerous services have sprung up that offer verification of email addresses in bulk.

High deliverability rate doesn’t mean that all of your emails sent end up in the Primary inbox. It may very well result in all of your emails ending in Spam. 

What do different status codes mean

In the next two tables, you can find an overview of the most common status codes along with their description and whether they are OK to send.

Status codeDescriptionSend
validThese are emails that we determined to be valid and safe. These will have a very low bounce (>2%).YES
invalid These are emails that we determined to be invalid, please delete them from your mailing list.NO
catch-allThese emails are impossible to validate without sending a real email and waiting for a bounce.WITH CAUTION

One such service is Zerobounce which offers highly accurate results which are handy when conducting cold outreach campaigns. These give you a clear idea of why you shouldn’t contact these email addresses. 

Status codeDescription
spamtrapThese emails are believed to be spam traps and should not be mailed. Sending an email to it might result in your domain being blacklisted.NO
do_not_mailThis is an umbrella term which includes the following status codes: global_suppression, possible_trap, global_suppression, disposable, Toxic,Role-basedNO
abuseThese emails are of people who are known to click the abuse links in emails, hence abusers or complainersNO
unknownService could not determine. Most likely invalidCAUTION
Find the full list here

I’d advise on selecting a service that provides the most elaborate set of status code and the lowest number of verifications with the unknown status code. It normal for each service to have a slightly different explanation for each status code.

Sending emails to only valid email addresses is the safest strategy.

Email addresses categorized with invalid status codes should be placed to your global suppression list. This is a list of contacts that should be prohibited from receiving any email communication. This protects you against mistakenly enrolling them in an email campaign in the future.

Global suppression list in a EMS

If you really must send emails to unknown and catch-all categorized email addresses – I’d highly recommend creating a separate segment just for them and progressively send in smaller volumes.

This way valid addresses will not get mixed with invalid ones and you will be able to quickly remove those that aren’t valid anymore. 

Many of the services have free tiers which are in many cases suffice. For instance, Zerobounce gives you 100 free credits each month.

If your database is a bit more sizable, you should expect to invest some money into premium tiers. To give you an idea, 5,000 verification usually goes for around $40 – hardly a significant amount for such an important aspect. Discount volume usually applies.

How to verify an emailing list

Verification of email addresses consists of the following steps:

  1. Preparation the CSV with email addresses to be verified
  2. Importing the CSV
  3. Running the verification 
  4. Analyzing the results

Preparation the CSV with email addresses to be verified

Firstly, we need to prepare a CSV file with email address information so we can easily import it to email verification too. 

If you have your leads in the CRM already you’ll need to export them to CSV file format – most of the CRMs will have this option.

Exporting Contacts’ data from CRM

I’d recommend creating a Google Sheet and paste all of your collected email addresses in a column named “Email address”. If you’ve collected information in CSV already but you want to process it before running through verification you can import it to Sheets with just a few clicks.

I like to keep the file as simple as possible. Since I’m exporting from CRM I have to fields in the sheet.

Sheet ready to be imported to Zerobounce

BONUS TIP 1: Exporting email address together with ID key is recommended – but not necessary. If you are exporting from CRM it makes re-importation a lot easier.

BONUS TIP 2: In case you’ve collected additional information such as the first name, birthday or company information you can include it in the Sheet.

Importing the CSV to ZeroBounce

Let’s export the Google Sheet into the CSV file. You can do this by clicking

File – > Download -> Comma-separated-values

Once you’ve exported the CSV file from Sheets, go to your ZeroBounce account and click on Upload your File and select just exported CSV file in the file browser.

Press Validate file

Uploading CSV to Zerobounce

This will take you to the next screen where you will need to validate your import.

Make sure that the column that contains email addresses matches the Zerobounce’s Email Address value as it does on the screenshot below.

Don’t forget to select Yes if your CSV contains the column name or header row.

Proceed with clicking Process File

Mapping the fields in Zerobounce

Analyzing the results

The time needed for verification will depend on the number of email addresses that need to be verified.

Keep that in mind if you have a sizable contact list – 1,000 and up – and you are planning to send out Newsletter in an hour!

Zerobounce gives you accurate estimation time to completion. Once finalised it shows a detailed overview of the verification.

You might be surprised at the results, especially if you have never done email verification on your list before.

Verification results in Zerobounce

By clicking on the left-most column (Filename) you’ll be able to download the results of the verification.

I’d highly recommend only using email addresses that have been marked as valid. Zerobounce does amazingly make it easy for us.

ZIP with email address group by status code

If you’re a visual person, check out *overview.pdf for a graphical of the results.

ZeroBounce provides a PDF overview of your verified list. It breaks down email addresses by ESPs (no surprise which is the most popular) and status codes.


Hopefully this post showed the importance of email address verification as well as the steps required to make a verification. 

Benefits of keeping your database are two-fold: 1) making sure that you have the best point-of-contact for each business and 2) keep your domain reputation healthy.

Ideally, you’d like to hook up these services to your CRM and let it validate the emails on a recurring basis considering that around 2% of your contact database, on average, decay each month.

If you have any questions on how to set it up, feel free to reach me on [email protected].

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