Bounce Notification – Types, what causes them, how to set up and how it works?

Bounce Notification – Types, what causes them, how to set up and how it works?

Posted under Developer , Email Delivery on November 15, 2017

We all have received emails with a bounce message in our mailboxes now or then. An Email Bounce is when an email doesn’t get delivered to the subscriber. The sender receives an email immediately indicating the Email Bounce. There could be a varied number of reasons why an email bounces. The email bounced could be either Hard Bounce ( permanent) or Soft Bounce ( temporary). The email message indicates the reason for the bounce as well. This is also known as Bounce Notification.

bounce notification email

Curious to know and understand all about Bounce Notifications? We’ve covered it all; what they are, how to set them up, causes for it and how to read it.

What is a Bounce Notification?

Bounce Notification is an automated message that is sent from an email system and informs the sender that the message could not be delivered to the intended recipient successfully. The notification contains either the non-delivery report of a failed email, failed delivery status, an error message or what error might have occurred and the non-delivery notification.

Email bounces must be closely monitored and managed. If the number of bounced emails increases, the sender reputation will be affected drastically.

Reasons for a bounce notification

There can be many reasons for receiving an email bounce notification; some common ones being email address has been changed, the domain has been changed, the mailbox is full, etc. However, the two main broad categories are –

hard bounce soft bounce

  • Hard Bounces – A hard bounce is an email message that has been rejected by the recipients server or could not reach the recipients server due to permanent non-deliverable conditions, such as;
    • The recipient’s email address is missing or invalid.
    • The recipient’s domain is non-existent.
    • Unknown recipient or error in typing the recipient’s email address.
    • The recipient has blocked your email address.
  • Soft Bounces – This is a temporary issue wherein an email message is able to find and recognize the recipient’s mail server and email address, but could not be delivered to the inbox. The email bounces back due to the following reasons;
    • The recipient’s inbox was full ( each inbox has a limit for emails to be received. When it exceeds the limit any further emails are rejected, until the user clears some space ).
    • The recipient’s mail server is down, connection timed out or network error.
    • The mailbox is abandoned by the user.
    • The email message was too long.

    In this case, either check with the recipient to resolve the issue on their end regarding inbox space and/or try to resend the email again. If the email continues to soft bounce in campaigns, the email address can be discontinued for further campaigns.

    1. Unknown user: This can be a reason when the mailbox exists no longer, mail provider is shut down or the email address is not valid or may be a portion of the email address is not valid.
    2. Full Mailbox: Each mailbox has a limit to store emails at a time and if that limit exceeds, the recipient’s server will reject any incoming email and it will be shown as a bounce notification in sender’s email box.
    3. Too Large Message: This happens rarely but still this is a cause of getting a bounce notification. The size of your email is defined by your service provider as well as the recipient’s service provider. Meaning of this bounce is you have written a mail which exceeds that defined size, which includes the header, text message, attachments, etc. In this case, too, the recipient’s server will reject the incoming mail for being too large than their defined size to accept.
    4. Did not Find Domain: This typically means that the domain your mail is intended to, does not exist or shut down.

    These are main causes of getting an email bounce notification. Other causes include – mail is trapped in a routing loop, domain’s internal issues like switching hosts, blocking of a certain type of IP addresses from recipient’s mail server, unknown or undefined reasons, etc.

    Actively managing your bounces is very critical, in case of hard bounces, deactivating them or adding them to a suppression list is highly recommended. This ensures that one will not accidentally send mails to email addresses that will certainly hard bounce. As for soft bounces, after some attempts at delivery, if the email continues to bounce then such email addresses can be transformed into a hard bounce.

How does the bounce notification work?

To understand the functionality of bounce notification, we need to understand the email flow first.

email flow
Image Source:

In the flowchart, we can see the journey of an email along the components. After passing through all the components, there is a handshaking stage. The SMTP server of the intended recipient takes a big role here, it helps to recognize the sender’s domain and make a contact with the receiving server. The recipient server goes through the message and checks the parameters mentioned above to give a green signal to the mail. If any of the parameters are missing, wrong or unknown, the recipient’s server rejects the email. Thus, the mail is sent back to the sender’s server and bounce notification is sent to the sender’s inbox.

How to read the bounce notification emails?

Bounce messages have specific formats and it is predefined by the mail server. Bounce notification can be a MIME multipart report message. It comprises three parts –

  1. An explanation in human-readable format.
  2. Delivery status which can be parsed by a machine. This includes a “name: type, value” parameter.
  3. The original notification message indicating the possible causes.


How to read bounce notification
Image Source:

How to set up bounce notification with Pepipost?

  • In Pepipost, to get bounce notification you need to navigate to Settings -> Customize -> Bounce Notification -> View Settings.
  • First, you need to create and Custom Envelop. To create a Custom Envelop you need to go to Domain Management -> Settings and create custom envelop to get bounce notifications.
  • With this, the bounce forwarding within your account is enabled. Now each time, when a bounce will appear, the system will automatically notify you. It will forward a bounce notification on the email address, which you have set for bounce forwarding.

To handle these notifications, you need to configure your app to receive bounces. For that, Real-time Event Notification API has to be enabled in the application. Also, the list of email bounces can be edited and retrieved through Web APIs of your service provider. You can handle Hard Bounces and Soft Bounces differently and you can do this through your account or APIs provided by your service provider.

An additional benefit of setting up these notifications is – it will also notify you about clicks, opens or anything that happened to the emails. So, you can easily calculate the response rate and improve your mailing campaign strategy accordingly.

We here at Pepipost are on a mission to build a cleaner email eco-system and are putting efforts to bring awareness and encourage good email sending practices. You can now switch to Pepipost and join the fastest growing good email senders community.

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Dibya Prakash Sahoo|The Business Guy

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