Let’s assume you send a letter to an old friend you’re no longer in touch with. The letter returns after a week with a stamp that says “undelivered.” Maybe your friend no longer lives at that address, was on vacation, or the postman failed to reach them. Email bounces are similar.
This article dives into the fundamentals of bounced emails, helping you get familiar with one of the biggest email deliverability and marketing challenges. So, if you’re a budding email marketer or entrepreneur working on your next campaign, continue reading to learn more about email bounces and how to avoid them.
What is an Email Bounce?
Simply put, a bounced email is an undelivered message. When the recipient’s email server rejects a correspondence, the sender gets a bounce message, which is also called a “non-delivery report (NDR)”. An email can bounce for several reasons, such as:
- The recipient’s mailbox is full
- The recipient’s email server identifies the email as spam
- The recipient’s email address is invalid or abandoned
When an email bounces, the sender gets an error message with the details. This is called a server mail transfer protocol (SMTP) response. Email marketing platforms deliver detailed bounce reports, helping you diagnose the problem. Depending on the company’s policies, they may automatically remove a recipient’s address from your email list.
What are the Contents of a Bounce Message?
A bounce message typically contains identification markers highlighting important information regarding the failed delivery. This can include:
- Reason for the bounce
- Date and time of rejection
- The affected mail server
For example, if you send an email to “name[at]xyz.com” and receive an error message “domain name not found,” it means either “[at]xyz.com” does not exist or “name” hasn’t renewed the domain.
Here are a few more examples of bounce messages.
- Delivery to the following recipient failed temporarily. Reason: Mailbox full
- Delivery to the following recipient failed temporarily. Reason: Unknown user
Types of Bounced Emails
Two primary types of email bounces are hard and soft, also called permanent and transient. A hard email bounce occurs when the recipient’s inbox provider rejects the message; a soft bounce results from delivery failure due to a temporary problem. Let’s delve into the details of them below:
What is a Hard Bounce?
A hard bounce is a permanent delivery failure. It occurs when the recipient’s email address is invalid or the destination domain is nonexistent. Common examples include typos like Gmial, Hitmail, Outlok, Yaho, or expired business domains.
Internet service providers (ISPs) monitor hard bounces and send an error message stating the reason for the failed email delivery. Different ISPs and mail servers use other response codes to distinguish between delivery failures.
Here are the common types of hard bounces and their fixes.
Recipient Doesn’t Exist
This hard bounce is a result of invalid email addresses. You should check the user and domain names and contact the user through a different channel to find out if they have a new email address. If the address still bounces after fixing the errors, we recommend removing it from your subscriber list.
Mailbox Full
Email service providers send this error message when the recipient’s inbox exceeds the maximum storage capacity. When this happens, you can contact the subscriber through a different channel, requesting that they clean their inbox. You must update all your mailing lists if they use a different email address.
Blocked Email Address
Mail servers employ several security protocols to check the sender reputation before accepting an email message. Failing to pass one of these triggers a hard bounce. If you receive a blocked bounce message from a smaller domain, contacting the ISP could help resolve the issue. For more extensive domains like Gmail, Outlook, or Yahoo, consult our experts for help.
Blocked by Spam Filters
Specific conditions might trigger spam filters on the receiver’s email servers. For instance, if a subscriber never opens your email, files spam complaints, or your messages contain spam trigger words. Launch a re-engagement campaign to generate interest if you notice that a subscriber hardly opens your emails. You should also avoid using spam trigger words in the subject line and body copy.
Consequences of Hard Bounces
Most mailbox providers monitor deliverability rates and sender reputation. Domains with higher deliverability rates are more trustworthy than those with higher hard and soft bounces. This matters since sender reputation significantly impacts email deliverability. Hence, you must always try to avoid hard bounces.
What is a Soft Bounce?
Soft bounces can cause a temporary email delivery failure. They occur when the recipient’s email server approves your IP and domain, but your message doesn’t reach their inbox. This happens when the message size is too large, the recipient’s inbox doesn’t allow emails from the sender, or suspicious and spammy content is detected.
Here are some common types of soft bounces and their fixes.
Mailbox Full
While a full mailbox is typically categorized as a hard bounce, it starts with a soft bounce. For example, you send emails to a subscriber who has interacted with your business before but isn’t responding to your current email campaigns. In that case, the ISP monitors the frequency of the failed emails for up to 3 days. Once the time limit is up, the ISP marks your emails as hard bounces. You can contact the subscriber and inform them about the exceeding inbox capacity or find out if they use a different address.
Challenge-response Error
A challenge-response error message appears when the user installs a filter to block spam emails. The filter automatically sends a challenge, usually an activity or a question. Your message is only delivered if you complete the challenge within the specified time. Double opt-in sign-up forms filter subscribers before adding them to your subscriber list. Run spam tests before broadcasting your email campaigns.
DNS Failure
A domain name system (DNS) failure takes place when the recipient’s email server can’t direct your mail to their inbox due to a technical issue. DNS issues may happen because of server downtime, typos, or a void destination domain. You can send your email after a few days. If the problem persists, contact the customer through a different channel and verify their email address.
Auto Reply Emails
Auto replies like out-of-office or vacation notices indicate that your subscriber is temporarily unavailable. These notifications are crucial when sending time-sensitive emails, informing the sender of the receiver’s unavailability. When this happens, you can usually contact the subscriber again after a few days.
Other Errors
Sometimes, ISPs don’t classify error codes when sending bounce messages. These are treated as soft bounces, as the exact reason for the bounce is unknown. You can contact the subscriber to find out if they have acquired a new email address.
Consequences of Soft Bounces
Soft bounces don’t impact your sender reputation immediately. However, repeated soft bounces will still affect deliverability rates. Most mail service providers enforce protocols to remove soft bounces after a while. For instance, some automatically remove email addresses that bounce more than 15 times.
How to Avoid Email Bounces?
Your marketing emails can only engage the audience if they reach the inbox. Hence, the success of your email campaign depends on its deliverability rates. Managing hard and soft bounces is crucial for email deliverability. Let’s walk you through email marketing best practices to reduce bounce rates.
Use Double Opt-in Forms
One of the best ways to improve the quality of your mailing list is to use a double opt-in form to validate new subscribers. A double opt-in asks for the subscribers’ consent before adding them to your mailing list. Most businesses refrain from double opt-ins since it takes longer to build an email list. However, double opt-ins ensure a higher-quality subscriber list and promote sustainable growth.
Maintain List Hygiene
High bounce rates are a sign of a poorly maintained email list. As your mailing list grows, you need to identify and remove inactive subscribers to minimize email bounces. Remember to check your feedback loops periodically and remove subscribers who report you as spam. Removing subscribers might seem counterproductive at first. But remember, it’s always quality over quantity.
Avoid Free Email Servers
Since spammers abuse these free services, email domains like Gmail are prone to DMARC, DKIM, and SPF authentication failures. As a result, your emails will more likely experience hard bounces. Moreover, sending business emails from a free server looks unprofessional and can hurt your brand image. Therefore, we always recommend using a custom domain.
Boost Your Email Deliverability: Minimize Bounce Rates with Expert Guidance
Growing a healthy email list is fundamental to every successful marketing strategy. You need a healthy subscriber list to improve customer engagement and generate business. Email list hygiene is a continuous process. Book a discovery call today to learn how our experts can help improve email deliverability and engagement while reducing bounce rates.
Head of Growth at Email Industries