This article explains how email bounces are handled within the Engage application. This handling is done automatically at a system level, but it is important to understand what happens when a message to a subscriber bounces, and the consequences of having too many bounces.

What is a bounce?

An undeliverable or bounced email is one that never arrives at the recipient’s mail server. When an email is sent through Engage, a recipient's email server either accepts or rejects the message. If the email server rejects the email, a bounce message is returned by the ISP to explain why they are unable to deliver the email to the intended address.

How are bounces classified?

When a message is bounced, Engage records the event and the reason why the message was returned.  There are four main categories of bounce events.

  • A soft bounce occurs when an address is temporarily unable to receive email. An email might incur a soft bounce if the destination mail server is temporarily not responding or a subscriber's mailbox is full. Engage will continue to attempt to send these messages for up to 72 hours until the message is delivered. If a message is continuously deferred for 72 hours, we record these as a single block bounce in Engage. Soft bounces themselves are strictly behind the scenes and not documented in Engage.

  • A block bounce typically occurs when an email server rejects the email due to filter issues, such as IP address blocks, lack of authentication, or when the sending domain or IP address is found on a blacklist.

  • A hard bounce occurs when an address is permanently unable to receive email. This typically occurs due to an incorrect email address, either because the mailbox no longer exists or the email address was mistyped.

  • Failed messages indicate a system error or temporary network failure that prevented the message from being delivered.

How are bounces handled?

If an address hard bounces, Engage automatically suppresses the subscriber and will no longer send to that address.

If the address returns a soft bounce, Engage will retry sending until the message expires (typically 72 hours). If the message continues to bounce after that time, then the message expires and a Block Bounce event is recorded.

A Block Bounce does not affect a subscriber's status or suppress them from future mailings. Messages that return a Block Bounce are not suppressed and will continue to be sent to in the future.

How does managing bounces affect reputation and deliverability?

Bounces can negatively impact your short and long term deliverability. One of the main factors that ISPs monitor to determine your sender reputation and ultimately the placement of your mail in a customer’s inbox is bounces.

Repeatedly sending to invalid email accounts tells ISPs that you are not following proper list hygiene practices - and that is a behavior common to spammers.

If the number of bounces for an individual ISP exceeds certain levels, you will begin to see message blocking or filtering into the spam or junk folder even for valid customer addresses. That is why it is important to remove invalid email addresses from your list on an ongoing basis.

How are out of office replies handled?

Out of office replies are not handled by the Engage system as bounces. Out of office replies are sent to the reply-to address specified in the sender profile used for that send. This is the same address where replies initiated by the recipient are directed for that campaign. This is often an internal email address monitored by your utility.