When you send out a cold email campaign, you often assume your customers got the emails. However, in many cases, the email might not even be delivered.

Sometimes, you’ll receive a bounce-back message explaining why the email wasn’t delivered. This is especially common if one of the addresses you emailed is invalid.

However, there are many reasons that your emails may not be delivered. In this article, you’ll learn what causes emails to not reach their destination and what you should do to ensure your cold email outreach successfully reaches all your recipients. 

What is Email Deliverability?

Your goal in an email marketing campaign is to get all your prospects to read your marketing email. This means they have to get to the recipient’s inboxes.

Email deliverability is the likelihood that sent emails will get into the recipients’ inboxes. This doesn’t include bounce-back emails you sent to invalid addresses or whose recipients’ inboxes were full.

There are many factors that can both positively and negatively impact email deliverability, which is why it’s important to know what to avoid and what you should do.

Reasons Why Your Emails Aren’t Reaching Their Destination

Chances are, you’ve sent emails that have not reached your customers.. Here are some of the most common reasons your emails aren’t delivered to recipients.

Invalid Recipient Address

This is the most common cause of email delivery issues. We’ve all been there: either you typed the email address incorrectly, or your source for the address was wrong.

Sending an email to an invalid address will result in a bounce-back message explaining that you sent an email to an email address that doesn’t exist.

Email Sent to Junk or Spam Folder

This is another common reason why your recipients don’t get your email. Most email services have a junk or spam folder that stores emails from known spam sites and other emails that just seem spammy.

While normal emails rarely go into the spam folder, some of your emails might have the same language or formatting as many other spam emails, so they’ll most likely be sent straight to the junk or spam folder.

While using spam triggers might not always send your email to the spam folder, it increases its chances, especially if you send it to multiple recipients.

The Recipient Server Blocked Your Email

Every recipient uses an email server to access and store the email you sent them. Sometimes, your email might be blocked by the recipient server if it has links to malicious or banned websites, malware, or viruses.

SMTP Settings

Even if you entered the right address and avoided spam and blocking triggers, your email might still not reach its destination if you have incorrect Simple Mail Transfer Protocol (SMTP) settings.

Several SMTP issues can prevent your email from reaching its destination. Below are some of the most common ones:

  • Authentication issues: Most SMTP servers require authentication to send emails. Therefore, the server will not send your email if your authentication details (address and password) are invalid or missing.

  • Domain authentication: Some email service providers use technologies like DKIM (DomainKeys Identified Mail,) SPF (Sender Policy Framework,) and DMARC (Domain-based Message Authentication, Reporting, and Conformance) to verify your domain. Recipient servers may block your email if your domain isn’t authenticated properly.

  • Incorrect Server Configuration: Incorrect SMTP settings like the wrong port number, server address, or authentication method can make it impossible for your client’s email address to connect to the server and send the email.

  • Blacklisting: If your SMTP server is on a blacklist for suspicious activity like sending spam, recipients’ servers will block your emails.

  • Content filtering: Some SMTP servers use content filters to detect spam emails. If your email contains spam triggers, it will be blocked before reaching its destination.

Malware Attack

Sometimes, you can get an email delivery failure message for an interaction you never initiated. In these cases, it’s possible that you were a victim of a malware attack, and a virus accessed your account and used it to send spam.

While email worms are becoming increasingly rare because of the strong malware-protection measures used by email providers, it’s still possible for malicious actors to access your account and use it to spread spam or malware.


Emails with attachments are often blocked by the recipient’s email server. Although common file types like DOCs, PDFs, and XLS spreadsheets typically pass through, sometimes they might encounter problems.

For example, sending an attachment with no subject or text to a new email address might be blocked or sent to the spam box.

Since there is the risk of malware being smuggled into an email through attachments, the recipient email server often blocks emails that contain them.

Tips to Enhance Cold Email Deliverability and Metrics

While some of the reasons above are unavoidable, there are some things you can do to ensure most of your emails get to their destination. The following are a few tips to improve your cold email deliverability.

1. Use a Better Email Software

If you’re using an email for business, it’s always advisable to have dedicated email software to help you manage to send and receive emails. A reliable email software offers features like crafting and sending targeted emails and increased deliverability.

For example, QuickMail can help you design and send cold emails at scale. You can personalize ice breakers, import prospect lists to the platform, and perform A/B tests to determine which works best for your target audience.

A good email software also focuses on email deliverability. While sending cold emails to your prospects is essential, ensuring the emails land in their inboxes is even more important. These platforms offer features to improve your reputation and avoid spam filters.

Platforms like QuickMail provides built-in error detection, blacklist monitoring, and auto-warmups.

2. Ensure Your Email is Warmed Up Properly

When you first open your email account, it’s not advisable to blast tons of cold emails to your prospects. In most cases, the recipient servers will flag your account as spam and block your emails.

Instead, it’s best practice to warm your email before starting a cold email campaign. This involves sending a few emails initially and gradually increasing the volume over time. 

You can use QuickMail’s autowarmer to warm up your email for free. QuickMail’s autowarmer will also give you a real-time score so you can see how warmed up your email is.

Alternatively, you can start by emailing friends and people you know to increase your account’s credibility. Emailing people you know also means they’ll reply, reducing your email bounce rates. This will prove that you’re not a spammer and eventually enhance your email deliverability when you start your cold email campaign.

3. Setup SPF, DKIM, & DMARC

SPFAuthorizes servers to send emails from your domain
DKIMVerifies that your email hasn’t been tampered with.
DMARCImproves your domain’s reputation.

SPF, DKIM, and DMARC are powerful trios that can help you get your cold emails into inboxes and avoid spam folders.

These protocols verify that you’re the rightful sender of the email. Here’s how:

  • SPF: The Sender Policy Framework (SPF) authorizes email servers allowed to send emails from your domain to prevent spoofing.

  • DKIM: DomainKeys Identified Mail (DKIM) adds a digital signature to your emails to prove to the recipient server that they haven’t been tampered with in transit.

  • DMARC: Domain-based Message Authentication, Reporting, and Conformance (DMARC) identifies unauthorized emails and strengthens your sender's reputation, an important factor in email deliverability.

4. Don’t Send Too Many Emails Too Fast

Sending a large number of emails in a short time period can result in your account being flagged  as spam or blacklisted. It is essential that you warm the email account sufficiently before you start sending cold emails in large amounts. 

And even after you’ve warmed up your email, you can still send too many emails. If you want to send many emails, though, you can simply buy multiple domains similar to your primary domain (that redirect back to your primary domain) and use those to scale your email volume.

So, instead of waiting to warm one domain before sending emails to your recipients, you can send emails using multiple domains for more volume.

5. Avoid Spam Triggers

Most spam filters check the subject and content of your email for words and formats that often appear in spam emails. Below are a few spam triggers you should avoid:

  • Spammy words: If your email has words that would be associated with spam emails, like free, fast cash, or call now.

  • Suspicious subject lines: If your subject has shady subject lines with excessive exclamation points and urgency-laden marketing phrases like “Hurry,” it alerts the spam filters.

  • Emails lacking subject lines: If your email is missing a subject line, especially when sent to multiple recipients or when it includes an attachment, it’s likely to be assumed to be spam.

  • Missing unsubscribe option: If you don’t give your recipients the option to unsubscribe from your cold emails, they’re more likely to mark them as spam.

While these are just a few of the most common spam triggers, avoiding them can go a long way in preventing your emails from being dumped into the spam folder.

6. Get Rid of Invalid Email Addresses Before Sending

Having invalid email addresses in your recipients will flag your account as spam. Therefore, ensuring all recipient addresses are valid before sending your cold email is essential.

While manually checking all the addresses is possible, it’s counterintuitive if you’re running a big cold email campaign. That’s why reliable email software is important.

Tools like QuickMail can verify all your addresses to ensure they’re valid before emailing. This reduces the risk of your account being flagged as spam.

7. Remove Emails That Give a Hard Bounce During the Campaign

Having a high email bounce rate hurts your domain’s reputation. Bounce rate refers to the percentage of emails that don’t get to their destination and bounce back instead.

Therefore, if you’ve received a bounce-back message from any email address, it's essential to remove it from your mailing list to prevent further bounces.

8. Avoid Heavy Formatting & Videos

Heavy formatting is often picked up by spam filters as a sign of spam. On top of that, heavy formatting may make your email harder to read, which reduces your cold email’s conversion rate.

On the other hand, most emails are opened on mobile devices. As a result, complex layouts with tons of HTML might not render properly, making your email a frustrating experience and making them mark it as spam.

9. Regularly Monitor Your Sender Score

Monitoring your sender score is like checking your email campaign’s health. It gives you valuable insights on your email campaign’s metrics like deliverability and engagement.

Your sender score is a reputation rating given to your account by email providers based on several factors. A high score shows users engage with your emails, while a low score edges you closer to being flagged as spam.

Here’s how monitoring your sender score can help improve your email’s deliverability:

  1. Targeted improvements: Analyzing your sender score can help you find areas for improvement in your email marketing strategy. For instance, low open rates can suggest stale subject lines or content.

  2. Identifying red flags: Analyzing your sender score will reveal potential spammy practices. For example, your bounce rate might be rising due to many incorrect email addresses.

Tools That Can Help You Improve Deliverability in Your Cold Emails

QuickMailAn all-around cold emailing tool with inbox rotation, deliverability testing, and inbox warmup tools.
Spamtester.aiAnalyze your cold email for spam triggers before sending it.
MailflowStimulates account activity by sending and replying to emails.

If you’re planning to run a cold emailing campaign, it’s important to have the right tools to maximize your email deliverability.

First, you can try an email warmup tool like Mailflow. These tools send and reply to emails from your account, reducing your bounce rate and improving your domain’s reputation with email providers.

You can also use a spam tester like Spamtester.ai. It checks your content for spam red flags like suspicious subject lines, overly promotional language in the content, and spam formats.

Finally, you can opt for a well-rounded tool like QuickMail. It is a cold email outreach program that offers all the tools you need to maximize your deliverability. 

QuickMail has a free native integration with Mailflow for warming and offers free DNS and blacklist monitoring for every domain you send from. Their advanced analytics give you better oversight of your deliverability and help you catch small issues before they become big problems. 

Frequently Asked Questions

How can I monitor and improve my sender's reputation?

The best way to monitor your sender reputation is by using email software like QuickMail. You can improve your sender’s reputation by:

  1. Warming up your account by gradually increasing the volume of your email sending.

  2. Reducing bounce rate by removing invalid addresses from your mailing list.

  3. Avoiding spam triggers.

  4. Boosting engagement with clear subject lines, and relevant, personalized content.

What are some best practices for email list management?

For healthy email lists, focus on quality over quantity. Verify new subscribers with double opt-in, segment your list for targeted content, and clean it regularly to remove inactive users. Track metrics and avoid spam triggers to improve deliverability and engagement.

What is a good email deliverability rate?

A good email deliverability rate means that most of your emails reach the recipient’s inboxes.

The exact rate depends on your campaign's goals. However, most cold email outreach campaigns are considered to have a good deliverability rate if it’s above 95%.

What is a bad email deliverability rate?

A bad email deliverability rate means that a significant number of your emails don’t get to the recipient’s inboxes. This includes bounce emails and those that reached the recipient’s address but were sent to the spam or junk folder.

In general, a bad email deliverability rate means less than 70% of the emails reach the inbox.

What’s the difference between a hard bounce and a soft bounce?

A hard bounce is a permanent delivery failure like an invalid address. On the other hand, a soft bounce is a temporary delivery failure, such as when the recipient’s inbox is full.

Ready to Skyrocket Your Cold Email Deliverability?

Cold emailing is a great way to increase conversions. However, to run a successful cold emailing campaign, you need to ensure your email deliverability is on-point.

While many factors might affect your email deliverability, you can improve it by warming up your email domain, avoiding spam triggers, and using good email software.

QuickMail gives you all the features you need to improve your account’s credibility and boost your cold email deliverability. So, what are you waiting for? Sign up today for a free trial and start sending cold emails.