In this blog, we explore the fundamental causes behind email bounces, from high spam complaint rates to invalid addresses or issues with spam filters. We also address technical difficulties, such as inaccessible servers or overloaded inboxes, that can lead to delivery failures. Additionally, we provide solutions and practical tips to overcome these challenges and ensure your emails reach their recipients effectively, ensuring better deliverability and success in your email campaigns.

You probably already know that there are different types of email bounces. If you're aware of their classification, it's time to understand why your emails are not being delivered. Let's get started.

1. High Complaint Rate

A high complaint rate is one of the main reasons why your email will end up in the spam/junk folder or get your IP blacklisted. Complaints are recorded when a user marks your email message as spam (by clicking the "Report as Spam" button).

Each ISP has a threshold for spam complaints, and if your email campaign crosses that line, your messages will never reach your user. This is because ISPs are strict about their customers receiving only wanted email.

2. Invalid Emails

One of the main issues is attempting to send emails to invalid or misspelled addresses. Due to recipients providing incorrect email addresses or unintentional errors in the email address book, such acts often lead to delivery failures.

Using the email address validation API from Valid Email is a way to address this problem on a large scale. With the help of this powerful real-time API, you can quickly find and correct any incorrect email addresses in your mailing list.

When the person associated with the email address has left the company, removing the contact is a circumstance that could result in a bounce marked as an invalid email address. Sending a message to a mistyped email address is another explanation.

Additionally, there is the possibility that recipients provide fake email addresses, especially if you collect contact information through online registration forms.

You can significantly reduce your bounce rate and build deeper connections with mailbox providers by implementing an API. Over time, this will enhance the effectiveness of your email communication by improving deliverability and ensuring your messages reach the intended recipients.

3. Spam Filters

Spam filters can be a problem as they label valid emails as spam, causing them to be forwarded to unintended recipients. This problem often occurs when emails contain specific keywords, suspicious attachments, or when the sender's IP address or domain has a poor sender reputation.

In some cases, spam filters can be blamed for the increased undelivered communications. None of your mass-sent messages are likely to reach the intended recipients and be received if you happen to use an email address or IP address that is blacklisted.

Visit our informative blog if you're interested in learning more about various spam traps and anti-spam strategies. It offers a guide and practical methods to navigate the complex world of email deliverability.

4. Server Issues

Email delivery problems can result from temporary server issues, maintenance tasks, or unforeseen server interruptions, both on the sender's and recipient's sides. Emails may experience delays, be postponed, or not reach their recipients.

Email delivery can also be hindered by network issues, as server connectivity problems can hinder message transfer. Delivery problems can arise from communication failures, as transmission and reception servers may have trouble connecting.

Messages marked as "undeliverable" are often called "soft bounces" and typically involve the recipient's email server being overloaded, temporarily down, or inaccessible. Waiting may be necessary before attempting to resend the email, as server unavailability may be due to maintenance or a breakdown. But many bounces of this kind can signal an ongoing server issue.

5. Overflowed Mailboxes

The mailbox capacity of your recipients can occasionally cause email delivery difficulties. Your message can exceed the allocated character limit if they have accumulated emails and attachments over the years without emptying their inbox.

In such circumstances, the email server may generate an "mailbox full" or "quota exceeded" error, causing the message to bounce back to the sender.

While it can be frustrating to send an email to a contact when their inbox is so full, this problem typically lasts for a short time. Once their inbox has enough space, you will likely be able to successfully transmit an email to the recipient.

6. Attachment Issues

Both the sender and the recipient may be subject to limitations on the type and size of attachments imposed by many email hosting providers. Most bounces are usually caused by these restrictions, often due to large attachments.

While it's generally a good idea not to add files to your email marketing campaigns, there are occasions when it's unavoidable. It's essential to remember that some email providers or email systems impose restrictions on attachment size.

Email may not be delivered or may bounce back to the sender if the attachment exceeds the allowed size. This can make it difficult to send important documents or information by email.

7. Blacklist

Your emails may be rejected or filtered if your IP address or domain is on a blacklist maintained by email service providers or anti-spam organizations. Inclusion on blacklists often occurs when a sender is found to be the source of spam or other abusive email practices, but it doesn't indicate that you're a spammer in all cases.

It could simply be a mistake.

Check our blog for tips on how to prevent your emails from going to spam if you want to avoid having your IP address or domain appear on these kinds of lists.

8. Permission-Related Issues

Your email list is where a good (or poor) email distribution always begins. A good list is created with strict permission requirements. Building an engaged audience can largely be done through a solid opt-in strategy.

However, just because permission was given once doesn't mean it will always be granted. You'll have to account for list fatigue and low response rates resulting from changing user needs over time.

You need your users to frequently open and click on your emails because ISPs now pay special attention to engagement rates. To maintain high email delivery rates, consider the following tips and best practices:

  • Ask for permission to keep sending emails to non-responders and systematically remove them.
  • Regularly request users to update their preferences in the preference center.
  • Make sure the unsubscribe option is functional and obvious.

In the end, users should deliberately unsubscribe from your list rather than mark you as spam. The latter causes problems for your email application by raising red flags with ISPs.

How to Prevent Your Emails from Bouncing

A high bounce rate is detrimental to your email list, significantly affecting deliverability and the overall success of your email marketing campaigns. It's crucial to closely monitor your bounce rate and be prepared to take the following steps if you notice some email addresses bouncing consistently. Visit our blog, where we provide valuable tips to prevent this from happening.


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