We’ve all received at some point in our inbox a message indicating that the email we just sent couldn’t actually be delivered. Well, this is a bounce email. Not appreciated in everyday life, it is even less so in the field of online marketing where deliverability is crucial!
In this article, we explore the reasons why emails bounce, as well as solutions to avoid this phenomenon and maximize the effectiveness of your campaigns.
Reminder on Bounce Emails
A bounce email (“Non-Delivery Report” or “NDR” in English) is an automatic notification generated by the recipient’s mail server to inform the sender that the email they attempted to send was not delivered. This notification usually provides information about the cause of the problem.
There are two main types of bounces:
- Hard bounce; it’s a non-working email address, so a permanent problem.
- Soft bounce; it’s a temporary issue preventing the recipient’s address from receiving your email.
As a sender, understanding the bounce message is essential, as it allows you to adjust your sending practices, better manage your lists, and improve the deliverability of your emails.
Why Do Emails Bounce?
Here are the most frequent reasons for bounces:
The Recipient’s Mailbox is Full
452 4.2.2 Mailbox Full
When a mailbox reaches its maximum capacity, new emails are rejected. This can be due to inappropriate message management by the recipient.
The Email Address is Nonexistent or Incorrect
550 5.1.1 User Unknown
This error occurs when the recipient’s email address is incorrect, nonexistent, or has been deleted.
Beware, it also often happens that the address entered during registration is incorrect.
The Mail Server is Temporarily Unreachable
421 4.4.1 Connection Timed Out
Errors of this type indicate that the recipient’s mail server is temporarily unavailable. This can be due to technical problems or server maintenance.
The Message is Too Large
552 5.3.4 Message size exceeds limit
If the size of the email exceeds the limit allowed by the recipient’s mail server, this can lead to a bounce.
The Sender’s Email Address is Blocked
554 5.7.1 Relay access denied
Some mail servers have strict anti-spam filters that automatically reject emails from unknown or suspected spammers.
Rejected as Spam
554 5.7.1 Message blocked due to spam content in the message
Anti-spam filters may mark an email as spam, leading to rejection. This can be due to inappropriate content, suspicious links, or a poor sender reputation.
There’s a DNS Problem
5.4.6 DNS Lookup Failed
DNS resolution errors indicate technical problems related to resolving the recipient’s domain name.
There’s an MX Problem
5.4.4 unable to route: no mail hosts for domain
The email could not be sent because the system cannot find the mail server for the recipient’s address.
Problems Related to Blacklisting
554 5.7.1 Service unavailable
If the sender’s IP address is listed on a blacklist due to suspicious activities or presumed spam, emails can be rejected.
Technical Problems at the Server Level
Temporary or permanent problems on the recipient’s mail server can cause bounces.
7 Simple Solutions to Avoid Email Bounce
1# Validate Email Addresses
Use email validation tools like Captain Verify to ensure that the recorded addresses are valid and well formatted.
By the way, don’t forget that it’s highly recommended not to buy or rent contact lists as these are used by several companies, and especially riddled with bad addresses, thus presenting a high bounce risk.
2# Rigorously Manage Lists
Good management of your mailing lists involves rigorous maintenance. Therefore, you should think about regularly updating them to keep them clean, which involves removing obsolete addresses and ensuring that your subscribers are active (remove the inactive ones).
3# Segment Lists
Segment your mailing lists based on your subscribers’ engagement, purchasing behavior, demographic data, or other information, to send more targeted and relevant emails.
4# Obtain Recipients’ Permission Before Sending
Make sure you have explicit permission from recipients before sending emails, which will reduce the chances of being considered spam while preserving your sender reputation. To do this, use double opt-in.
5# Personalize and Care for the Content
Create personalized and engaging content to encourage interaction, but also to show your recipients that you know them. This will greatly reduce the risk of being marked as a malicious or unwanted sender. In the same vein, avoid using sensitive words that might trigger anti-spam filters.
6# Authenticate the Email Account
Implement authentication mechanisms such as SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance).
These protocols help verify your authenticity as a sender, thus strengthening your credibility and keeping you out of the spam folder.
7# Monitor the Bounce Rate
Use analysis tools to regularly monitor the bounce rate of your campaigns. A sudden increase in this rate can indicate potential problems requiring immediate intervention.
Correcting email bounce and maintaining a low rate is essential to ensure the success of your email campaigns. By analyzing and understanding the causes of bounces, then implementing the suggested practices above, you can greatly improve the deliverability of your emails.
