Understanding bounce messages

Let’s take a guess: You spent hours and hours crafting your next email campaign. When you felt ready to send it out to your subscribers, you pressed the "send" button and enjoyed the feeling of accomplishment that comes from a job well done.

For some weird reason, though, when you went back to see how your campaign was performing, you got the shock of your life. You realised that you had an alarming bounce rate and you were left disappointed and questioning yourself.

If this is you, don’t worry. You’re not alone. We know that as a marketer, you probably have a rough idea of what email bounces are but you might not be sure how to avoid them.

What is an email bounce?

  • An email bounce, is a message that cannot be sent to its intended recipient. Email servers are unable to send emails for a variety of reasons such as the recipient has changed their address
  • The recipient address mailbox is full
  • The email is incorrectly addressed.

When an email cannot be sent a non-delivery report is sent to the sender each time a server rejects a message to let them know about the bounce. You may have seen this yourself. Although these bounced messages do share the same information, their appearance will differ depending on the inbox provider.

A bounce message often consists of the following:

  • A message alerting the user of the bounce error
  • Details regarding the day and hour the email was bounced
  • Data containing the particular ID of the bounced message
  • The server's IP address and hostname
  • Error message from SMTP

Soft and hard bounces

Soft Bounce

An email message that is soft bounced is one that reaches the recipient's mail server because the email address is recognized but is returned before it reaches the recipient. This means the email had the ability to be delivered but failed to do so.

A soft bounce may happen for a number of reasons, including:

  • A full mailbox (over quota)
  • A down or overworked server
  • A large message
  • A user abandoning the mailbox

Most email service providers will make repeated attempts to transmit the message for a few days. A hard bounce occurs if the message is still undeliverable.

Hard bounce

A hard bounce raises the most serious issues because it suggests a persistent problem that hinders message delivery. A hard bounce is an email that comes back to you because the recipient's address is incorrect. A hard bounce would never deliver as it’s permanently undeliverable.

A hard bounce can happen for a number of reasons, including:

  • The domain name not existing
  • The recipient not being known
  • The address being incorrect (due to typos or a change of address)
  • The email recipient's mail server blocking your server
  • A network issue on the recipient's end

What to do when your emails bounce because of the following:

1. Full mailbox

When an email bounces due to a full mailbox, it means that even though the recipient's email address is valid, the mail server rejected the message. Most email servers and mail hosts email servers and mail hosting companies place restrictions on the size of data that can be held within an email account.

Solution: You could resubmit your message a bit later if it's not time sensitive because this issue will resolve as soon as the recipient gets more space in their mailbox.

2. Domain not found

If you send a message to a domain name and it was returned as Domain Not Found, the domain name is invalid. In most cases, this implies you made a typo on the domain name.

Solution: Check the spelling of the domain name.

3. User unknown

User unknown bounces happen when the destination email address is invalid or has been closed, or when the email address's domain is no longer active. When a person leaves a company, switches to a different ISP, or makes a typo in their email address, this commonly happens.

Solution: Try to get in touch with the person you were trying to email by other means to make sure the address is correct. Most of the time, people don't realise they have supplied an incorrect email and that their emails aren’t working until someone else notifies them of the problem.

4. Message exceeds size limit

This type of bounce indicates that your email is too large to be received because it exceeds the domain's maximum per-message size restriction, which includes all headers, text and attachments.

Solution: Try to make the message smaller or break it up into smaller pieces before sending it again.

5. Spam

Although system administrators often configure their systems to reject spam, since no spam filtering system is completely flawless, your email might have been mistakenly blocked as spam. It indicates that the domain name of your provider is specifically listed on a blacklist as a known spammer. This could be due to a third-party service that gives ISPs access to blacklists of known spammers, or the administrator could have put a ban in place due to the high volume of emails coming from your domain.

Solution: You should speak with your provider as soon as possible since, in most cases, they will need to speak with the system administrator to have the restriction lifted.

6. Connection timed out

High mail processing volumes at the time your message was received often cause a "Connection Timed Out" bounce. The domain's email servers may block connections or disconnect connections before a message is entirely delivered as a result of the server getting more mail than it is used to, an external attack on the domain, or an internal configuration issue.

Solution: When the issue is fixed, you will be able to send your mail without any issues because mail exchangers are configured to only take as much mail as they can manage.

Some general tips to avoid bounces

1. Make sure to regularly clean your email lists

Making sure that your mailing lists are routinely cleaned is one of the best ways to guarantee that your email bounce rates are kept to a minimum. Maintaining proper email list hygiene is essential since it assists in removing contacts who are inactive or uninterested in reading your content.

You have a better chance of raising your open rates, deliverability rates, and engagement rates while lowering bounce backs when you regularly clean your email databases. You will benefit from having a better sender reputation as a result of all of these factors. This is always advantageous to marketers.

2. Use double opt-in to your advantage

Using the double opt-in email setting can help you. When new subscribers must immediately confirm their email addresses it can lead to more false signups or even just typos occuring. By using double opt-in you can safeguard against this happening.

3. Ensure your domain is authenticated

SPF, DMARC, and DKIM are the three main protocols used to authenticate emails. Generally these email authentication standards are not always when people start their email marketing journey.

The main reason you should verify your domain is to send positive signals to your email contacts receiver security system to prevent them from flagging your domain. Verification enhances sender reputation and in turn increases email deliverability rates as fewer emails bounce.

Gain more understanding of the benefits of domain authentication in our guide.

Key takeaways

You should rely on your email marketing platform to inform you that your messages haven't reached their intended recipients and what kind of bounces occurred.

Bounces can help you to understand why your emails may not be achieving the desired results you are looking to achieve. Having too many bounces will lower your important email metrics like deliverability rate and sender reputation. The good news is that you can take steps right away to lower your bounce rate and make sure your emails have the best possible possibility of arriving in the intended inboxes.

By using the advice in this article, you can take the necessary actions to lower your bounce rates and enhance your email marketing performance.

Have any more questions about email bounces? Ask us in the comment section below.


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