29 january 2025, 13:41 
A well-planned outreach campaign may still fail due to a challenge many businesses underestimate – email deliverability issues. It’s not that simple for an email message to wind up in a recipient’s primary inbox. When spam filters sideline it or bounce it back due to suspicious content or incorrect configurations, the impact can be far-reaching. You risk losing conversions, erode customer trust, and damage your sender reputation.
Read on to find out how to troubleshoot email delivery issues and learn about practical steps for identifying and fixing them.
The Notion of Email Deliverability
The term refers to a message’s potential to reach a recipient’s inbox. However, it may not be possible for different reasons, such as the sender’s prior reputation or the content of the message itself. The success of email delivery is measured by the percentage of messages accepted by receiving servers.
Some may misunderstand the concept, thinking that delivery and deliverability are the same thing. The difference here lies in the following:
- Email delivery: validates that the sent mail has actually been accepted by the subscriber’s mail server and did not bounce.
- Email deliverability: determines the number of emails that actually reached the inbox relative to the total number of messages sent.
The high deliverability rate indicates that all the efforts you put into the promotional campaign will not be in vain. It is also important for other reasons that we’ll discuss further.
The Importance of Email Deliverability
A high delivery rate shows dependability and confidence. Problems with email delivery reduce an email campaign’s efficacy. Customers are more likely to engage with your business if they often get your notifications in their inboxes.
It is also important to consider some other crucial parameters that indicate the significance of email deliverability:
The brand’s reputation
Landing in spam folders can tarnish your brand’s image. Consequently, decreased visibility in recipients’ inboxes will lead to fewer opens, clicks, and conversions.
Likewise, ISPs and email services monitor emails flagged by users as spam or suspicious. If many people mark your emails as “junk,” the algorithms interpret that as a negative signal. They then adjust their filtering rules and eventually make all future messages head straight to the spam folder.
Improved ROI
Apart from brand visibility, it is essential to reach the main purpose of the email campaign, which is to increase the company’s profit. Failure can be painful because, as recent studies show, emails can bring as much as $36 for every dollar spent. Maximizing deliverability ensures your marketing budget and resources are spent effectively.
Long-term growth
When all your emails reach the inbox, it means your content is viewed, and more people engage with it. It also connects both sender and receiver, creating prospects for future emails to be delivered properly and not to be lost. Moreover, each successful send may augment the subscriber list and drive traffic and conversions. Investing in deliverability will surely have a positive outcome in numbers.
Now, we need to see the common types and reasons for email delivery problems.
Hard Bounces vs. Soft Bounces vs. Server Unreachable
It’s essential to understand the fundamental types of mail delivery failure. Generally, these issues fall into one of three categories: hard bounces, soft bounces, and the receiving server being unreachable. Though they all signal a failure, each type has unique causes.
Soft bounces
These bounces indicate a temporary problem with email delivery. It may occur when the receiver’s mailbox is packed with messages or when a server has temporary delivery problems.
Hard bounces
This is a permanent occurrence. Such problems are typically caused by spammy email content or indicate a mailbox that no longer exists. It is important to note that a reliable email service provider should restrain you from repeatedly sending messages to unreachable addresses. Sending multiple emails that hard bounce hits the sender’s reputation.
Server Unreachable
In this case, the email is not delivered due to issues with the recipient server. The usual reasons are server maintenance or connectivity failures. Such failures typically do not affect your sender reputation, however you’ll still waste time and money if you do not monitor such issues.
Let’s go a bit deeper and see what provokes them.
Causes of Soft Bounce
As we already know, it is usually a temporary appearance and can be solved without changing the email strategy. Below are some common causes due to which it can occur.
Too many emails
If you send a high volume of emails to a specific domain within a short time frame, the receiving server may temporarily defer these emails to manage server load or see whether users will tag you messages as spam.
Suspicious content
Email filters detect keywords that could be considered spammy (like “guarantee”, “100%”, “giveaway”, etc.). Of course, some may be delivered, but if the system is unsure, the message will usually be put on hold.
Greylisting
Some email servers use it to reduce spam. The server rejects the first email attempt and only accepts subsequent efforts from the same sender. This approach forces automated spam bots to drop off, as they usually do not retry sending.
Soft bounces are usually taken care of automatically. A good ESP will retry sending or spread greylisted emails over time to ensure they are all eventually delivered.
Causes of Hard Bounces
The occurrence of hard bounces is linked to permanent reasons, and down below, we will take a closer look at them.
Non-existent recipient address
That is a pretty obvious reason. If you try to approach a recipient who does not exist, it will result in a failed attempt. If the address has a typo, the result will be the same. Fortunately, with the email validation API, you can check whether an email address is correct before sending an email to it without harming your sender’s reputation.
Keep in mind that people may abandon or remove their mailboxes for different reasons. Over a year, up to 15% of all addresses in your list may become unreachable. Such addresses should be promptly removed from the list, as abandoned mailboxes are often repurposed as honeypot spamtraps.
Spam content
Overstuffing the message with spammy words, deceptive subject lines, or excessive exclamation points can result in hard bounces. ISPs’ spam filters get increasingly sophisticated, too, so trying to disguise an actual spam message is not an option at all.
Missing SPF, DKIM, or DMARC authentication
Every day, a server blocks batches of emails and marks them as spam. Most of the time, this is not a mistake. However, nothing is perfect, and even impeccably crafted messages may appear there too. One of the main reasons behind this is improper or missing authentication.
Make sure you’ve set up Sender Policy Framework (SPF), Domain Keys Identified Mail (DKIM), Domain-based Message Authentication, Reporting and Compliance (DMARC) records in your domain’s DNS. Otherwise, certain email systems may mark your message as junk. Major mailbox providers like Gmail and Yahoo are making email authentication a strict requirement.
High bounce rate history
Internet service providers also track user behavior when accepting your messages. Consistently high bounce rates signal that you’re sending to stale or purchased lists, encouraging providers to block future messages as a protective measure for recipients.
Blacklisting
If your domain or IP address shows up on popular blacklists as a result of spam complaints or sending unsolicited bulk emails, most servers will immediately reject your messages. Regularly checking reputation monitoring tools and promptly addressing issues will help you stay off these lists.
Large email attachments
If you try to email some presentation or another file that exceeds the size limits of the receiving email server, the message will be rejected. Alternatively, use file-sharing services and provide a link so your email stays slim.
Permission-based issues
Trying to approach recipients who unsubscribed from your mailing list or never opted in can result in complaints and eventual hard bounces based on server rules. Similar filtering rules may be created by addressees themselves to avoid unwanted mail. Again, such addresses need to be removed from your list as soon as possible.
Standards violation
Email servers will verify email structure according to a number of standards like RFC guidelines and check for faulty MIME formatting. Offending messages won’t be accepted. If you use your own software to craft automated messages, double-check to ensure they are formatted properly.
Mailbox capacity issues
It is mostly a soft bounce issue, but persistent attempts might transition to a hard bounce. If the same address always yields a “mailbox full” SMTP status, it should be treated as unreachable.
Fixing Email Delivery Issues
Your business should improve its email output using the following tactics to prevent and fix email delivery issues. In order to address all of the above issues, the following steps need to be implemented as part of a successful email strategy.
Improve Sender Reputation
Your sender reputation has a significant impact on deliverability and improving it can help troubleshoot email delivery issues. If the score is low, you will experience mail delivery failures every time you try to reach your auditory. Here’s what you can do:
- Exercise consistency in sending emails. Keep off sudden spikes or long pauses in your email volume. Being silent for months and then blasting out thousands of emails in a single day can create problems. Instead, distribute your sends over time so providers recognize a stable, predictable sending pattern.
- Use reputable IPs and domains. Make sure the IP address and domain you use for sending aren’t blacklisted.
- Avoid spam complaints at all costs. If the subscriber doesn’t want to receive your emails, provide an easy way out by including an “unsubscribe” link. High complaint rates can quickly ruin your reputation, so always respect recipient preferences.
Configure Email Authentication Protocols
It is vital to prove to ISPs that you are who you claim to be. This reduces the chances of your emails getting filtered out as spam or phishing attempts.
Sender Policy Framework (SPF) is used to specify which servers are authorized to send emails on behalf of your domain. Without it, you risk getting intruders that can forge your domain in spam campaigns.
DomainKeys Identified Mail (DKIM) uses digital signatures to ensure that your messages haven’t been modified in transit. Should your email be subjected to any changes, the signature check will fail. Then, servers know the email has been tampered with.
Domain-based Message Authentication, Reporting & Conformance (DMARC) is a way to notify receiving servers what to do when an email fails SPF or DKIM checks. It can be configured to quarantine (put in spam), reject, or do nothing if the message doesn’t pass. The latter option should be enabled only temporarily when you change your email setup.
Clean Your Email List
You have to keep your list of recipients clean. Make sure you’ve got rid of all the invalid addresses. In return, your emails will have better open and click rates and less email deliverability issues. Also, you can do the following:
- Consider inactive audiences. If you’ve sent them your emails before and got no engagement, try one more time. If there’s still no result, clear them from the list.
- Use double opt-in. Adopt a confirmation link for new subscribers. They will need to click the link before they can be officially added to your list. Such an approach will secure the right recipients and save you from spam traps, typos or accidental sign-ups.
Optimize Email Content
Perfecting the technical aspects of email is essential. However, all your efforts may be useless if it looks suspicious or is filled with spammy words. Do the following:
- Focus on high-quality content. The messages you share should be clear and structured. Avoid spam-like phrases so they won’t trigger the spam filters. The content should be engaging and informative, with relevant and working links.
- Focus on a balance of plain text and HTML. Plain text and well-structured HTML help email clients correctly interpret and display your messages. A good balance of text and images can also reduce the likelihood of your emails being flagged as spam.
Monitor and Adjust Sending Practices
Once you’ve done all of the above steps, you still need to keep an eye on how your emails perform. Here’s what to do:
- Track bounce rates and complaints. If you see an increase, investigate immediately. For instance, if some domains reject your messages, adjust your approach as needed.
- Segment the recipients. Sending the same message to all of your subscribers may not be efficient, as not all are equally interested in the same topic. Divide them into smaller groups of interest to send more relevant emails. Higher relevance means better engagement, which, in turn, supports stronger deliverability.
- Perform A/B testing. Experiment with different subject lines, preview text, templates, or send times. It will help you find out what resonates best with each audience segment.
All of these approaches will help you to troubleshoot email delivery issues. With them, you’ll lay the groundwork for stronger email performance.
How can UniOne Assist with Email Delivery Issues and Boost Your Business Growth?
Though it may sound trivial, you really need a reliable partner to help you with email delivery. UniOne is an all-in-one solution for email delivery with a proven track record of excellent deliverability. It provides a detailed dashboard with real-time monitoring that displays sends, deliveries, opens, clicks, and bounces.
As to the technical peculiarities, the service provides SPF, DKIM, and DMARC configurations for proper setup, so adding the crucial DNS records will be easy. Also, UniOne’s API documentation is straightforward, allowing easy integration into your applications for transactional emails and marketing campaigns.
If you are looking for a creative and hassle-free HTML builder, UniOne has something to offer here as well. The HTML builder will help you to create visually attractive templates for different activities. Email elements can be easily drag-n-dropped or edited via HTML code. Alternatively, you can create your own from scratch or use an AI assistant.
UniOne is built to manage high volumes of emails, so you don’t run into delays or throttling issues. It is a straightforward partner that will provide backup for email deliverability issues.
Сonclusion
Email deliverability is a critical component of modern marketing and communication strategies. When email delivery issues arise, you risk losing users and conversions.
As you pinpoint the issues and find a way to fix them, you can make email one of your most reliable methods for customer communication and growth. And if you want to make this path even easier, choose UniOne and be sure that all your message will reach your audience.
