Email Bounces

Email Bounces

Bounces occur when sent emails cannot be delivered. Typically, the email server will send you an error message, detailing the reason for the bounce.

How bounces occur

Once an email is ready and the 'Send' button has been clicked, the system immediately looks up the recipient's domain and mail server. Once our system makes contact, the mail server looks at the message to determine if it will deliver the message. If the message passes through the mail server, then it is considered a success. If that server finds that the email address is invalid or does not exist, then the corresponding bounces will be returned back to our sender's server. This is called a 'hard bounce'.

If the recipient's email address exists but does not have enough storage space to accept the message, then it will bounce back to the sender as a 'soft bounce'. There is a possibility that these bounces may have occurred while the recipient system is busy or unable to handle requests. These emails will be retried within the next five days.

Our system will identify the mail delivery status based on the recipient system's response/status code/message, then generate a report for it.

Significance of bounce rates

Bounce rate has great impact on your domain reputation. Internet Service Providers (ISPs) and Email Service Providers(ESPs) set a certain threshold for bounce rates; exceeding that threshold may lead to a warning or account suspension.


Bounces come in two categories: soft and hard bounces.

Soft bounces

A soft bounce is just a temporary delivery failure.It does not necessarily mean the email address is invalid or no longer active, so we will continue trying to send emails to these addresses.

Common reasons for a soft bounce

  • Recipient's mailbox is full
  • Email server is temporarily unavailable
  • Email content is too large
  • Spammy content or blacklisted sender address

If a particular address is bounced for three times as a 'soft bounce', it'll be considered a hard bounce. It will be added to the 'Bounced' list in order to preserve server and IP integrity.

Soft bounces = temporary deliverability failures                                                                                                                                                                                                                 

Hard bounces

A hard bounce means there is a permanent reason for the delivery failure. Generally, the recipients' addresses are immediately added to the 'Bounced' list. Frequent hard bounces bring down the reputation of sending sources drastically.

Common reasons for a hard bounce

  • Recipient email address does not exist
  • Domain name does not exist
  • Typos (for example, instead of
  • Recipient email server has blocked delivery
  • Inactive email address
  • Email account has been closed

A raise in hard bounce rate badly affects your sender domain reputation with ESPs and ISPs, and may also lead to blacklisting of your email address.

Hard bounces = permanent deliverability failures                                                                                                                                                                                                             

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