13 most common email deliverability issues and how to solve them

‍Email deliverability can make or break your email campaigns. So if your messages aren’t reaching the inbox, it doesn’t matter how great your content is: it’s not getting seen! 

To help you with this common problem, we’ll talk about the 13 most common email deliverability issues that businesses face and, more importantly, how to solve them. Authentication problems, low sender reputation, spammy content, blacklists (such as the Sorbs DUHL Blacklist or the Suomispam Reputation Blacklist), here is what you need to know to ensure your emails reach your audience where it matters.

What are email deliverability issues?

Email deliverability issues are simple: your emails are landing in spam instead of the inbox. That’s it. No matter how compelling your message, if it’s stuck in the spam folder, it’s not doing its job. 

There are many reasons why this happens, such as poor sender reputation, misconfigured authentication records like SPF or DKIM, using spammy content, or even sending too many emails too quickly. But at the end of the day, all these factors lead to the same outcome: your emails aren’t being seen. 

So for any business relying on email for communication or sales, this is a huge problem. It means lost opportunities, wasted time, and reduced impact. The goal is to : 

1. Understand these issues,
2. Fix them quickly so your emails land where they should: right in your recipient’s inbox.

Common causes of email deliverability issues

If your emails are ending up in spam, there are usually a few key culprits. But at first, you must understand these common causes to be able to fix the problem properly, and get your messages into the inbox. 

Here are the main reasons why your emails might be hitting the spam folder, based on our experience at MailReach:

• Poor sender reputation: If your email address or domain has a history of low engagement or high spam complaints, your sender reputation takes a hit, and your emails are more likely to end up in spam.
• Incorrect or missing authentication records (SPF, DKIM, DMARC): Email providers can’t verify that your emails are legitimate without proper authentication, which makes it easier for your messages to be flagged as spam.
• Spammy content: Keep in mind that there are some “spam words” to avoid in your emails, like “buy now” or “free,” excessive punctuation, or too many links. Even using all caps or too many images can hurt your deliverability.
• High bounce rates: Sending emails to outdated or invalid addresses leads to high bounce rates, which signal to email providers that your list isn’t well-maintained. And yes, this can quickly get your emails flagged as spam.
• Sending too many emails, too quickly: A sudden spike in your sending volume is a HUGE red flag, as it looks like you’re spamming, especially if you’re sending to a cold list.
• No clear unsubscribe link: If recipients can’t easily opt out, they’re more likely to mark your emails as spam. The result: it damages your sender reputation and makes it harder for future emails to reach the inbox. Bad impact.
• Using a shared IP address: If you’re using an email service provider with a shared IP, your deliverability can significantly be affected by the actions of other users on the same IP. One bad actor can ruin it for everyone.
• Lack of engagement: Do not forget that low open rates, few replies, and little to no clicks also signal to email providers that your messages aren’t valuable.

How to fix your email deliverability issues

Step 1 - Run a free spam test using MailReach's Spam Test

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To resolve your email deliverability issues, the first step is understanding exactly what’s going wrong. That’s exactly why we built the MailReach Free Spam Test, a powerful tool designed to evaluate where your emails are landing and pinpoint any issues affecting your inbox placement. How? We’ve analyzed tens of thousands of emails and identified the most common problems, so we know what to look for.

This test is completely free to use, up to three times per day, and doesn’t require you to create an account. Just copy a small snippet of code into your email and send it to a list of provided test addresses. 

Good to know: You need to replicate the exact conditions under which your emails ended up in spam, or the results won’t be accurate! The MailReach tool will then analyze your email, providing a comprehensive spam score along with insights into its performance across major email providers.

You’ll receive a detailed report, scoring your email on a scale of 1 to 10, along with specific recommendations to improve your deliverability. This includes checks for common issues like missing authentication records or spammy content. The goal is simple: give you a clear understanding of where your emails are going wrong and how to fix them.

Remember, you can’t fix what you don’t measure. So running this test is the quickest and easiest way to get a handle on your email deliverability and start making improvements that matter. That’s it.

Step 2 - Follow the recommendations of the Spam Test's report and run a new one

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You’ve run your first spam test and now have your score. Great. You know exactly where your emails are landing and what’s holding you back. Now, it’s time to act. 

Check the “Content” and “Setup” tabs in the report for specific issues, whether it’s a missing SPF record, spammy phrases in your email, or broken links. And fix these issues immediately.

Once you’ve made the changes, run another test to see if your score improves, because this isn’t a one-and-done process. Keep testing and refining until you hit that 10/10 score. I

f you’ve fixed everything and still can’t get a perfect score, your sender reputation might be the problem. It’s a clear sign you need to focus on rebuilding trust with email providers. But for now, follow the report’s advice, test again, and get your emails out of the spam folder and into the inbox where they belong.

Step 3 - If you're still in spam after making the changes, email warm up is your best option 

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If you’ve followed all the recommendations from MailReach’s Spam Test and your emails are still landing in spam, it’s a clear sign your sender reputation is in trouble. No amount of tweaking your content or adjusting settings will fix this on its own. Your email activity needs to show providers that you’re a trustworthy sender, and that’s where email warm-up comes in.

You have two ways to generate the engagement needed to rebuild your reputation. The manual way involves sending emails only to your most engaged contacts, crafting messages that get opens and replies, and slowly rebuilding trust over time. It works, but it’s time-consuming and doesn’t guarantee quick results.

But the smarter, automated approach is to use an email warm-up service like MailReach. 

It’s designed to do the heavy lifting for you by generating real engagement from real inboxes. Once you connect your email account, MailReach starts interacting with other inboxes, sending emails that get opened, replied to, and even pulled out of spam. The result: it creates a steady flow of positive signals to email providers, which is fundamental to show that your messages are valuable and deserve to land in the inbox. Nowhere else. 

Discover the best email warmup tool for a perfect deliverability

If your reputation is damaged, there’s no faster way to rebuild it. You can also check out our dedicated guide: “How to Restore a Bad Sender Reputation and Deliverability Using MailReach”!

Step 4 - Read our (No BS) deliverability guides to improve your inbox placement

We’ve spent years analyzing email deliverability data and refining strategies to help businesses like yours get their emails where they belong: in the inbox. Based on this deep experience, we’ve put together no-nonsense guides that cut through the fluff and give you actionable advice you won’t find elsewhere. These aren’t generic tips you can get from a quick Google search: these are real-world strategies proven to work.

Start with our Ultimate, No Bullshit, Email Deliverability Guide to understand exactly How to Prevent Emails From Going to Spam, covering the ins and outs of email authentication, content optimization, and sender reputation management.

If you’re doing cold outreach, our Best Cold Email Sending Strategy guide is a must-read. It’s packed with specific tactics tailored to cold emailing, in order to help you engage new contacts without tripping spam filters.

Good to know: These guides are built on real data and tested methods that have helped countless businesses improve their email success. Read them, implement what you learn, and you’ll see a noticeable difference in your inbox placement!

Why do I keep getting mail delivery failure emails?

If you keep getting mail delivery failure emails, it simply means that your messages are bouncing back, and that’s a problem. These bounces can be divided into two main types: soft bounces and hard bounces. 

• Soft bounces are temporary issues, like a recipient’s inbox being full or the server being down. They can often resolve themselves. 
• But hard bounces indicate permanent problems, such as a non-existent email address or a block from the recipient’s server. So ignoring these can seriously harm your sender reputation and affect your deliverability.

There are countless reasons why emails bounce, and listing them all here would be impossible. But the most common reasons include typos in email addresses, outdated contact lists, and getting blocked by spam filters.

If you’re dealing with specific bounce-back errors like 550 High Probability of Spam from Gmail, or 550 Permanent Failure, you’re not alone. Our detailed guide are at your disposal to help you deal with these issues!