Making sense of bounces


Undelivered messages, otherwise known as bounces, is one of the more complex topics in email marketing. Given that the notion and handling of bounces goes back to the earliest days of email it's not surprising that there's a lot of confusion and misunderstanding regarding them.

What is a bounce?

In short, a bounce is a message that could not be delivered to the intended recipient. While the reasons for non-delivery vary, bounces will represent the portion of a campaign that did not reach it's target. For a complete summary of the various bounce categories, refer to our bounce type guide. The categories can be distilled to three major groups; hard bounces, mail blocks (soft bounces), and general soft bounces.

How are hard and soft bounces different?

Hard bounces represent a very specific type of bounce, an invalid address. These are messages which were explicitly rejected by the target server because the address does not exist. They are considered permanent failures. For example, a message sent to, would be returned as a hard bounce because there's no user 'bob' at our domain.

Soft bounces represent every other bounce. They are temporary failures. For example, if you sent a message to domain with no active mail server, a soft bounce would be generated. In other words, the message couldn't be delivered, but it might be delivered at a latter time.

How do bounces affect senders?

Bounces are a good indicator of the overall health of campaigns and lists. High bounce rates tend to indicate old or poorly maintained lists, or poorly executed mailing efforts. If high bounce rates are sustained for an extended period, the reputation of the sending domain will suffer.

What bounces should I be most concerned with?

Hard bounces are the worst bounces to see on a bounce report. They indicate either an aging list (addresses have been abandoned and are being deactivated) or poor list collection practices (single opt-in, transcribed addresses). High hard bounce rates indicate a fundamental problem with list data and will quickly derail even the most thoughtfully organized campaigns. Hard bounces are unavoidable, some subscribers will abandon addresses leading to a hard bounce, but regular list hygiene can help counteract typical list attrition.

How should bounces be managed?

Effective list and bounce management begins at the list's origin. Using only a confirmed opt-in process (sometimes referred to as double opt-in) is the best way to insure that only valid addresses are added to a list. Confirmed opt-in (COI) works in this way: When a new subscriber submits their address for addition to a mailing list, a message with a unique confirmation link is immediately sent to the submitted address. Only when the subscriber clicks that link is the address fully activated in the list. This insures that the only addresses in the list are those who have expressed serious interest in receiving messages.

Regular review of campaign bounces is also required to keep lists clean and efficient. In ReachMail hard bounces are immediately deactivated and can be considered automatically cleaned from lists. Soft bounces, such as 'mailbox full' bounces and DNS failures should be monitored and occasionally acted on. For example, an address which bounces three times in a row with a full mailbox error is a good candidate for deactivation from a list. This is an address which has likely been abandoned or is being used as a catch-all by the end-user. It's best to deactivate it.

How should an existing list be handled to minimize bounces?

For more in-depth discussions, please refer to our guides on List Uploading Best Practices and Porting a List. In short, apply any possible rules to the list to reduce it to only the most likely active recipients. For example, an online retailer might pare down their list to only those customers who have ordered in the last 60 days rather than send to every customer from the past 5 years. While this may significantly reduce the initial list size, this is a good time to reflect that the most effective email marketing campaigns are built around quality not quantity. A greater effect is garnered by sending to 500 active, engaged subscribers than 3,000 disengaged subscribers.

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