10 Reasons You Need to know for Why Emails Bounce
Written by
Ninad Pathak
Ninad Pathak

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10 Reasons You Need to know for Why Emails Bounce

Published : May 21, 2020

Email bounce rate is a very commonly used metric in the email marketing industry. But what are the reasons why emails bounce? In this article, let’s discuss some of the most frequently observed reasons why emails sent out during campaigns bounce.

Emails bounce. But they bounce for a reason (and it’s not because they love it!). Before finding ways to fix bounces, we need to figure out why the email isn’t being delivered. So we spent some time analyzing the bounced emails, their responses and came up with the top 5 reasons why emails bounce and don’t get delivered to the intended email addresses.

1. Wrong recipient email address

For some really strange reason, this turned out to be the #1 reason across the industry. I’m still surprised that it holds such a major chunk of the email bounce percentage. Going deeper, we figured that it’s not entirely your fault if emails are bouncing due to wrong email addresses.

If you’ve locked your content behind an email signup wall, or require an email to download a piece of content, quite a few people use temporary email services that are available out there.

Apart from that, another common reason for this is if you’re majorly working in a B2B industry.

In such cases, users who registered with their official email addresses, and then left the company will have their email address deleted.

Based on what the attrition percentage in your industry is, your list could have a good number of dead email addresses.

How to fix this?

Keep an eye out for hard bounced emails. With Netcore Pepipost, you get easy visibility into the delivery status of emails. You can export all the bounced emails and use them as a suppression list on our platform without any hassles to prevent reaching out to the dead emails over and over again. Remember, get rid of dead emails from your list before they get your domain reputation down.

2. Spam Filtering

The days of rule-based spam filtering are long gone. Most of the users now use Gmail (we see over 55% user base on Gmail), Outlook, or Yahoo.

And all of these mailbox service providers have moved way past the rules-based filtering and incorporated artificial intelligence and machine learning algorithms for spam recognition.

Compared to the older methods, machine learning algorithms create new rules by themselves with no human intervention needed. So even a hint of “spam-ness” in your email can get that particular email to bounce. To add to it, a bad sender IP (this depends on how well your email service provider maintains their IP reputation) can assure that your emails will be rejected or blocked by the algorithms automatically.

How to fix this?

The first and quickest way is to find out how many of your emails bounce. Then try them in a different campaign. If another email reaches fine, the bounce was specific to the email being sent.

If that gets blocked too, dive into the bounce response and see if it was a hard bounce or soft bounce. With us, you’ll be easily able to see if an email bounced due to permanent reasons or temporary ones and also if some of them were marked as spam.

These insights help you understand where the fault lies and quickly fix them. And this brings us to our next point.

3. Recipient Inbox is Full

Some mailbox providers, specifically seen with people using company email addresses, have limited inbox space. Once the storage quota is full, the user must clear their mailbox to receive more emails.

We’ve seen this change over the last few years because of the wide acceptance of cloud storage and email services like GSuite, Office 365, Zoho, etc that offer virtually unlimited email space for each mailbox. But then again, due to compliance, some companies still work with on-site servers that have limited space availability.

How do you work around this issue?

There’s not much that you can do here. Just wait for the user to clear their inbox because they’ll have to do it sooner or later. You also don’t need to do much on your part in suppressing their emails like we would need to do for a hard bounce. Take a break of a day and continue to send them the emails they opted in for.

4. Bad Sender Reputation

Sender reputation is a combination of both the IP and the domain reputation. The domain reputation is completely in your control. The IP reputation can be shared between multiple users of a bulk email service (unless you decide to use a dedicated IP).

Now, why does the sender’s reputation matter? It helps spam filters make a quick decision on whether to accept an email from a sender or not.

For a majority of the email senders, a shared IP environment suits perfectly as long as you maintain your domain reputation. But you need to ensure that you choose the right email service provider who knows how to take care of their IP reputation.

How to maintain domain and IP reputation?

The domain reputation is under your control and we have shared quite a few posts on how you can improve your reputation using warm-up campaigns, the heartbeat campaign, and more.

Apart from that, if you’re a new sender on our platform, you will notice that there are milestones set up for you before you begin sending your emails in bulk. We’ve designed the platform in a way that helps you improve your domain reputation at every step.

And, we take care of the IP reputation by only onboarding genuine email senders. If our manual verification team deems that a specific domain that was added to the platform could spam or send cold emails (which does spoil IP and domain reputation), we monitor their metrics closely to confirm the same.

If confirmed, the domain is no longer allowed to send emails from our platform. After all, we don’t want someone else’s bad sending behavior to affect your genuine marketing efforts whatsoever.

5. DNS Verification Records Incomplete

We’re surprised this made it to the list of the top 5 reasons for email bounces. Adding SPF, DKIM, and other DNS verification records is a very important step and there’s no bypassing this in the long run. Maybe a few campaigns of yours could be delivered correctly but at some point, you’ll start getting blocked.

If the majority of your users are on Gmail, there’s just no way your emails are passing through the spam filters without these records set up. If you don’t know what this is, make sure you read through the post on SPF and DKIM records.

How do you fix this?

You need to chat/call with the support team of your email service provider and get the record details from them. Each of these records is automatically generated strings that look like random characters typed together and can be provided by the people handling your email servers.

With us, you’re very unlikely to fall into this issue because our platform requires that your domain is verified with both of these records before you begin sending emails.

6. Email blocked

If a subscriber blocks your email address, it’s best to consider it as a hard bounce, and stop sending emails to them. Just like sending an email to the wrong email address, there’s not much you can do from your end in this case. And taking any sly steps here trying to bypass the block will only hurt your reputation further.

How do you fix this?

When you figure out that your email address has been blocked by some of your subscribers, the best thing to do is take a step back and see why this happened? It would need your subscriber to be really annoyed to go ahead and block you. It’s nothing to be sad about, but surely something to consider analyzing.

  1. Does your email have an unsubscribe link?
  2. Did the user really opt-in for your emails?
  3. Are the emails relevant?
  4. Are they too frequent or too infrequent?
  5. Does the customer trust your brand?

These are some of the questions that you should start with while analyzing what you’re sending out to your subscribers.

7. Blacklisted IP

In the very unlikely scenario that your IP is blacklisted by mailbox service providers, your emails will automatically bounce and not reach your customers. There are a few things that you can still do in this situation for an IP blacklist but it’s always best to take steps beforehand to avoid the IP blacklist.

You can check if your domain/ IP is blacklisted – Email Blacklist Tool

How do you fix this?

If you’re using a bulk email service provider with shared IP and it gets blacklisted, the bulk email service provider you were working with hasn’t taken the right steps to maintain it. In such cases, it’s best to find a better ESP who knows how to take better care of their IP reputation. At Pepipost, we only onboard genuine businesses and reject domains that do not fit the screening criteria. So the IP that you share on our platform will be with some really high-quality email senders.

Apart from that, you also have the option to opt for a dedicated IP so you can take complete control of your IP.

8. Message Too Large

Marketing template emails can increase in size as we include images, add some attachments, add fancy graphics, and much more. This is fine up to a certain point (start optimizing if your emails start going beyond the 500kb mark). Once it goes above the max size the server accepts, the email will be rejected by the receiving servers outright. The best option is to have very well optimized email templates that are really tiny in size.

How do you fix this?

This one’s easy. You just limit the size by using CDNs to deliver images and graphics, and instead of directly attaching files to emails, add links to the files which are uploaded on some kind of cloud storage.

9. Ignoring Email Responsiveness – (not a major issue, but still important!)

Trends continue to change. What’s accepted now in marketing, will probably be a “practice of the olden days” in some time, and marketers have to keep up with trends. Here’s a trend that started a few years ago but has now become a necessity when emailing.

  • Mobile Responsiveness

Not having a mobile responsive template won’t break your email campaign and land you in the spam folder. But it sacrifices user experience.

More than 60% of your email subscribers will view your email on their phones. And if they have to zoom and scroll horizontally and vertically, they’re not putting in the effort to read it. They might as well zoom in to find the unsubscribe button once and for all.

How do you fix this?

Move away from using fixed sizes, to percentage sizes while designing templates. You can specify the size in the percentage of the block that should be occupied by specific elements.

This not only makes it very easy for you to view the templates on all the devices while maintaining complete visibility, you no longer have to worry about coding templates for all screen sizes. One template built with percentages will fit all the device screens.

Marketing evolves by the day. And marketers have to keep an eye out for what’s new, what’s no longer acceptable, and what can be improved upon. Following the same practices for years is not something that a good marketer will practice. Keep experimenting and trying out things to see what sticks with your user base.

3 things apart from the list above that you should find ways to incorporate in your email campaigns starting from today.

  1. Personalize, Personalize, Personalize – There’s no escaping personalization in any form of marketing. Generic mass marketing no longer works and people are way too used to that to pay any attention.
  2. Make Emails Interactive – Let’s take turns to speak, is much better than I speak, you listen. When customers speak, they tell you things that will grow your business exponentially! So speak less, listen more. Make your emails interactive and ask for responses.
  3. Add interactive media like videos, audios, animations – Static images are all good and everything but videos will convey a lot more information than a static image. But do this only depending on your brand’s voice. We want people to remember your brand’s personality and all branded media should portray similarly.


These are just some of the many reasons why we see email bounces. If your emails bounce for any reason, there will always be steps you can take to ensure that your bounce rate is maintained at the lowest possible rate. Be sure to check out some of our recent blogs related to email bounces and how to maintain a good sending reputation to ensure that your delivery and inboxing rates are super-high!

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Written By: Ninad Pathak