Why do emails bounce?

An email is declared as Bounce when it directly comes back with an error message: it means that it is not delivered.  Depending on whether they are temporary or permanent, the errors can be soft or hard bounces. 

There are two types of bounces which are handled differently as explained below: 

Soft Bounce: This is a temporary issue such as the recipients inbox is full, the email message is too large, or a connection timeout. 

We will automatically attempt to resend the email. If it cannot be delivered after a certain number of attempts, the recipient will be “Blocked” for 90 days. After the 90 days, the email address will be active again.

Hard Bounce: This is a permanent delivery error which can be caused by the following: 

  • An invalid email address (e.g. a mis-typed email, the email no longer exists -  i.e. the person has left the company or a non-existent destination server - it is not a valid email or domain name). 
  • Emails can also hard bounce if the recipients email server rejects the email and so it is blocked from being sent to the recipient. 
  • This may happen if the recipients email server runs spam checks and also DNS checks, for instance if SPF or DKIM records are not set up then the email can be rejected by the email sever - even if it is a valid email address. 
  • The recipients email server may also look at the IP addresses of the email server that the email is coming from - if the IP address is found on a blacklists then this can be why the recipients email server rejects the email and so it is blocked. 

Hard bounces negatively impact your sender reputations and are automatically blocked. 



What is an acceptable bounce rate?

8% or below is an acceptable bounce rate any higher than this would indicate that your data is old with email addresses no longer being current.

Why do emails get blocked?

This occurs when a bounced email becomes a hard bounce (i.e. we have tried many attempts to deliver the email but it cannot get through for the reasons described in the bounced section above). 

After 90 days a bounce if not delivered becomes marked as blocked.  An email is blocked when it has no chance of getting to your recipients inbox. 


A blocked email is therefore not sent: this avoids to uselessly hurt your sender reputation by causing an error on the recipients server.


Please note that to decide if it blocks an email or not, our system uses data from the history of your sending and several other parameters. 


Here are some examples of what causes emails to be blocked:


  • A recipient reported you as spam or unsubscribed from your e-Marketing campaign - in either case these email addresses will automatically be blocked.
  • A recipients address has already hard bounced and therefore will be blocked.

Emails that previously have failed will be blocked - this could be for reasons such as the email account no longer existing or an invalid domain. 

To find out more please click here to read the section on Email Reporting where you will find a guide to understanding the e-Marketing report statistics or alternatively contact our Support Helpdesk.