If you’ve been sending email campaigns over the past few years, you’ve probably noticed that it’s a lot harder to reach the inbox. Maybe your open rates aren’t what they were. Maybe your bounce rates are climbing. Seeing those undeliverable messages is more than frustrating. While we may want to point fingers or fix the problem immediately, the first step is understanding the problem.

How and why has email deliverability changed? That’s a complicated question. It’s so complicated that we felt it was necessary to write an entire eBook on the subject. However, with the changes that are happening it’s more important than ever to understand how email messages are processed. When you send an email blast to 1,500 people and 200 of your messages bounce, it’s time to inspect why your messages are bouncing. Believe it or not, your list almost certainly didn’t contain 200 nonexistent email addresses. Emails are rejected for several reasons, and trying to message an undeliverable recipient is only one of them.

Understanding complicated technical processes can be intimidating, but it doesn’t have to be that way. After all, when it comes down to it, sending an email is really just trying to deliver a package to someone.

Calling Ahead

If you were trying to deliver a regular package to someone in person, you’d probably want to verify their address before driving across town to deliver the package. That’s what email verification tools can do- they call ahead without actually sending a message. While email verification services are valuable pieces of marketers’ tool sets, they aren’t perfect. Why is that? Because email verification only works for a percentage of corporate email servers. Companies can set up their emails to handle pings (calls) in different ways. There are two primary ways that email servers handle requests.

SMTP-based Validation

Companies that allow you to check if an inbox is valid without having to send an email permit SMTP-based verification. Anyone can ping the email address to find out whether the inbox exists or not. This is the best case scenario- you’ll know whether you have the right address or not.

Accept-All Email Servers

Companies that use this configuration tell you that absolutely every email address at that domain is valid. They initially accept all messages, and then check to see if it’s valid. That’s not very useful because while they’ll tell you that your friend lives there, they’ll tell you that Donald Trump lives there too. Calling or pinging these servers is waste of time. There’s a reason that companies set their server like this. They want to keep strangers (spammers) from dropping off packages at the house. They’re betting that the only people who’ll drive all the way to the house to drop off a package are the ones who know who lives there.

So those are the two primary scenarios for verifying addresses without sending a message. If a company’s server is configured to accept all messages, you’re going to have to try and deliver the package to see if you’ve got the right destination.

Delivering the Package

There’s several causes for your emails not reaching your recipients. Bounces come in many shapes and sizes. Understanding these rejections and why they happen is the first step to becoming an expert at launching email blasts.

Hard bounces

Hard bounces occur when the address is undeliverable. It simply does not exist. The server lets you know via an email back to you. It’s like you walk up to the front door and you’re told your friend doesn’t live there (recipient unknown). Or maybe you drive there and there’s no house at that address (domain doesn’t exist).

Sometimes hard bounces are unavoidable. According to MarketingSherpa, 2.1% of B2B emails decay each month. That means a flawless list of 1,000 valid email addresses in June will likely have only 979 valid in July. DiscoverOrg guarantees its data is 95% accurate (and not 100%) for this exact reason- sometimes it takes weeks to learn that someone have moved on.

Soft bounces

Soft bounces indicate a temporary delivery issue, not a permanent one like with hard bounces. There are several types of soft bounces that can impact the delivery of your emails, unlike hard bounces, which are relatively straightforward. Let’s take a look at some of the most popular reasons for soft bounces:

DNS Failure

This may happen if an email server has been misconfigured or if the server is down. This is treated as a temporary issue because correcting the configuration or getting the server up would then render the email address deliverable.

Exceeding Attachment Limit

We’ve all seen this one. Most email servers have size limits and when a message arrives. If that limit is exceeded, the message will bounce.

Mailbox Full

You may think of voicemail when you hear “mailbox full”, but this happens to email boxes too. The recipient inbox has likely exceeded its quota, which means there’s no room for your message.


Sometimes your recipient email address is valid, but your message is not welcome. This can happen in several ways.


This can happen if your reply-to address, domain, or IP address is blacklisted. When you attempt delivery from a blacklist, your mail can get blocked and rejected by the email server.

Known Spammer/Spam Detected

Email blocks also occur if the server suspects that you are a spammer, either due to your domain or IP address. Additionally, your message may be blocked if it contains suspicious content usually found in spam messages.

Relay Denied

Your emails may return with this bounce notice if you do not have proper authentication for your message. Improper or nonexistent authentication is a red flag and email servers often reject such messages. Configuring SPF, DKIM, and DMARC is always recommended to give your messages the best chances of being delivered.


Now that you’ve been educated on the different reasons emails don’t reach the inbox, what can you do about it? There’s a few things:

  1. Monitor domain and IP reputation to ensure you aren’t on a blacklist
  2. Set up SPF, DKIM, and DMARC authentication for all of your email sending methods
  3. Do not use words or phrases commonly used by spammers
  4. Utilize data that is accurate and constantly updated

Doing these four things will put you in an excellent position to successfully send emails to your recipients. Unfortunately, only doing three of these things will likely put you in a hole that’s awfully tough to dig out.

To find out more about how DiscoverOrg’s continually refreshed, human-verified data can revolutionize your email campaigns, Request a Demo to see our platform which contains the most accurate data in the marketing and sales intelligence industry

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Derek Smith
About the author

Derek Smith

Derek was DiscoverOrg’s first researcher in 2007 and now a decade later he’s responsible for the processes and technologies that DiscoverOrg’s research team uses to create and update the data in our industry-leading sales intelligence platform.