How Often Should You Verify Your Mailing List

How Often Should You Verify Your Mailing List

Email verification is an important process when you’re sending emails at scale. It helps you filter out invalid addresses from your list and only contact verified recipients, which builds a positive sender reputation.

But email addresses don’t stay verified forever, and as this article will show, email data decays sooner than you might think.

As people change jobs, their old email accounts get removed, making their addresses invalid. And companies increasingly decide to set up accept-all mailboxes as a way to combat spam.

This is important because sending emails to invalid or accept-all addresses will inevitably result in a higher bounce rate.

It’s also important because sales organizations rarely clean the contact information sitting in their CRMs.

In fact, I ran a survey before publishing this, and 62% of respondents said their CRMs never get cleaned. If that’s the case for your company, you might be using email addresses that haven’t been verified for years.

And as my recent experiment shows, even if you carefully verify your list of email addresses, it only takes a couple of months for your mailing list to decay to the point where it’s risky to contact.

Why email verification statuses decay

Email verification is a complex process with multiple steps.

The most superficial checks include analyzing the syntax of the address to see if it’s valid and whether it’s a webmail address (e.g., or or a professional address (e.g.,

The results of these checks will not change over time because they are directly related to the character string that constitutes the address.

However, more intricate verification checks can prove whether the email address exists and if it’s ready to receive emails. This can change over time as mailboxes are deleted by the administrators of a given domain, and some domains change their settings to accept-all.

What are the consequences of using stale email data

The problem with using old email data isn’t just that your emails won’t reach their recipients.

It’s also that, in some cases, they will bounce back, damaging your sender reputation.

The consequences depend on whether the given address became invalid or accept-all.

If it became invalid after you verified it, your message will bounce back and you’ll damage your sender reputation.

On the other hand, if it became accept-all, then it’s likely still “valid” under the hood – meaning that the mailbox that used to be verified as “valid” still exists, but the server configuration was changed to accept-all. In this scenario, your message is admittedly less likely to bounce right away. However, you can no longer be sure that it is still fully safe to contact.

In any case, by contacting a decayed mailing list, you’ll:

  1. Miss some prospects – and you won’t always know which ones, because you won’t always get a bounce-back message.
  2. Damage your deliverability for any future campaigns sent from the same email address and domain because of a lower sender reputation.

About my experiment

With these consequences in mind, I wanted to find the answer to the following question:

How often should you re-verify your mailing list to avoid a high bounce rate?

Or, looking from a different perspective, how soon after verifying your list should you send your campaign?

Answering these questions would help me establish a best practice for how to collect, store, and use email contact information.

To find an answer, I started an experiment that lasted for two months:

  1. I went to LinkedIn Sales Navigator to build a mailing list in a transparent way. I used the following filters:
  2. Location: North America
  3. Job title: SDR/BDR and a selection of C-level titles like CEO, COO, CTO, VP.
  4. After finding several thousand prospects, I looked for their email addresses using Hunter’s Bulk Email Finder.
  5. I exported all the valid email addresses that Hunter found, excluding accept-all addresses. This left me with 1278 valid email addresses.
  6. I re-verified the entire sample weekly for 8 weeks using the Bulk Email Verifier.

How long an email address stays valid

After 8 weeks, 2.3% (29/1278) of my sample was invalid. If I sent a campaign to these recipients, my emails would bounce back.

Moreover, 3.2% of the email addresses were reconfigured as accept-all. While they are less likely to bounce, it’s no longer possible to fully validate them – and as time goes on, they would become increasingly more risky to contact along with the growing possibility that the underlying mailboxes were removed.

In total, 5.5% of my mailing list was no longer valid after 8 weeks.

Week 1

Week 8













Note: The "unknown" status can occur when a given email server temporarily blocks Hunter from verifying an email address.


This simple experiment shows that email data gets stale very quickly.

I didn’t expect that over 2% of my list would no longer be valid after just four weeks, which means at least 2% of my emails would bounce if I sent a campaign to these recipients.

(2% is a recommended bounce rate threshold for cold emails – if your campaigns get a higher bounce rate, you should consider scaling them back to troubleshoot deliverability first.)

This means that you should verify your mailing list shortly before targeting it with a campaign.

With Hunter, you can verify your email addresses at the very last minute while setting up your campaign.

Use this feature if your mailing list hasn’t been recently verified!

It's also worth noting that if you're using a CRM to store leads, you should regularly re-verify the data or export and verify it shortly before sending a campaign.

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Ziemek Bućko
Ziemek Bućko

Content Manager and cold email evangelist at