Bounce back emails make unpleasant reading for any marketer. You can spend hours crafting the perfect outreach email, only for the message never to reach the intended recipient.
What’s more, these notifications signify a problem with your email list. If one email address is wrong or out of service, how many more could be inaccurate?
To get to the root of the problem, it’s important to understand why you’re receiving bounce back emails, and what you can do about it. In this guide, we’re going to explore both topics in depth.
What Exactly Is a Bounce Back Email?
A bounce back email, also known as a Non-Delivery Report (NDR) or a Delivery Status Notification (DSN), is essentially an error message. It tells you that an email you just sent did not reach a working inbox, and provides a few details about the problem:
- The issue that has caused the bounce
- A unique email ID
- The time when the bounce ocurred
- The hostname and IP address of the recipient server
- An error message or SMTP error code
With individual messages, an occasional bounce is nothing more than an inconvenience. When you’re sending thousands of messages in an email campaign, a high bounce rate can be a major problem.
Emails may bounce for a variety of reasons:
- The Incorrect Email Address: If you misspell a recipient address or send to a non-existent email address, the message will bounce.
- Mail Server and Domain Problems: A misconfigured email server or email domain can cause messages to be rejected.
- Capacity and Policy Limits: A full mailbox will return to the sender. In addition, some email accounts are set up to reject certain types of incoming email (e.g. messages that break file size limits).
- Security Filters: Email accounts will sometimes reject messages that look like spam or some kind of cybersecurity threat.
We will take a closer look at each of these issues later, along with some key troubleshooting steps.
4 Common Types of Email Bounces
Not every bounce back email is exactly the same. In fact, there are four different categories of bounced messages and associated error codes. Some indicate a temporary issue, while others tell us there is a permanent failure.
Soft Bounce (4.X.X Error Codes)
A soft bounce is caused by a temporary delivery issue, such as email server downtime or an inbox that has reached maximum capacity.
When your email client receives a soft bounce notification, it will probably try to send your email again several times within the next 72 hours, in the hope that the problem will clear.
Hard Bounce (5.X.X Error Codes)
At the opposite end of the scale, we have a hard bounce. This type of bounce back message denotes an issue that isn’t likely to be resolved any time soon. For instance, resending an email to an address that doesn’t exist is a losing game.
Transient Bounce (Usually 4.X.X Codes)
A transient bounce is a variant of the soft bounce, where the problem might only last minutes. Classic examples include server downtime for maintenance, network issues, or a server that is overloaded with requests. As with a soft bounce, your email provider will respond to such notifications by trying again.
Unspecified Bounce
There are occasions when the reason for a bounce isn’t clear. This can happen when a server provides an ambiguous error message, or doesn’t respond at all. Unspecified bounces can be tricky to deal with, because it’s almost impossible to diagnose the underlying problem.
What Is an Acceptable Email Bounce Rate?
When you’re sending email messages at scale, some bounce back is inevitable. Most marketers consider 2% as a benchmark. However, it’s worth remembering that bounce rates are like limbo dancing. The best go low.
While the exact figure varies across industries, a study of one million marketing campaigns from verified accounts found that the average email bounce rate was 0.3%. Other research suggests that this average figure tends to rise as emails become more infrequent.
