A bounce or delivery status notification is the medium used by mail servers to communicate delivery problems to humans. Unfortunately, the only humans who understand the messages, known as bounces, are people who eat, sleep and breathe email communications. Your typical email server manager will not likely be an expert in this field. Bounces don't follow a consistent format. In fact, there are over one thousand seven hundred different formats recognized today by those who study email deliverability, and the number is increasing. Those who work with email application servers do their best to make sense of these messages for their applications, so they can take the appropriate action for each message. This article discusses the methods and reasons for managing bounces effectively.

Why should we manage bounces effectively?

Failure to properly handle bounces will penalize you with ISPs efforts to defeat the myriad of spam that is sent every day. ISP’s, many times, monitor the number of hard bounces in relation to messages delivered and change deliverability status or even blacklist a sender with a high ratio. This is done because spammers use the email infrastructure to harvest email addresses by attempting delivery to random addresses. They then remove bounces to build a list of deliverable email addresses. You may breach the threshold just by failing to clean an opt-in list for a long period of time.

Many who use email have subscribed to challenge response services to shield them from spam. These services require a sender to verify the email was from a valid source and that it was sent from an actual human. The sender must then visit a portal and enter characters displayed in images. But what happens when one of your customers generate an important transactional, business critical, email which is returned as a challenge response?

Another business critical reason to start handling bounces now is a new buzz. Feedback loops for email senders use the same bounce format to convey important matters such as spam complaints to the sender. If you correct problems reported in the feedback loop, you earn points toward the score at the ISP, or email service provider. Your reputation is protected by a point system. These messages are intended to be read by humans, but could also be processed in the same way as bounces are currently managed.

Spam complaints from AOL, for instance seem to be useless to most, since they don't disclose the original recipient, but the original recipient might actually be found in these messages, using standard bounce processing methods. The complainant could then be removed permanently from any lists without human intervention. A single spam complaint from an individual will not hurt your reputation, deliverability or your overall return on investment. ISP’s recognize that people subscribe to lists and then forget and then may prefer to report the email as spam rather than unsubscribe. Attempts to unsubscribe from a spammer’s list simply verifies your address to the spammer and is typically unsuccessful. Your address is then added to many other lists and the circle of spam fuels itself.

If you send email in bulk regularly and you don't handle bounces, you can be assured that most of your email will not be delivered at some point in the future. The definition of bulk is quite loose, as a blacklisting can occur after only a few hundred or a few thousand messages. That could be the one newsletter you send this year about the company picnic. The result is now problems for customer service.

We know why to manage bounces, but how do we?

Since there are almost two thousand, ever-increasing, bounce formats, the dreaded regular expression will be an important component of any viable email application server. In fact, there will be a very large number of regular expressions to run on each message. I know there are a few of you who actually enjoy crafting regular expressions. Don't even think about it! Take a look at the following products built by coders who do nothing but study bounce formats and the regular expressions that match them. You'll still have plenty of opportunities to extend the matching capabilities with your own set of expressions.

Two products for handling bounces are BoogiePOP, and b*Bounce.

These products work on slave machines by reading messages from a POP address and running the messages through a series of regular expressions. If matched, there are options to store the bounce information in a file or database. Sorting through the records in the database or file and taking action is the responsibility of an application developer. We've used both products and you might also use both, since they are different and one likely has better customer service. We didn't experience any problems getting answers from either.

XMS mail server offers an option to use the b*Bounce library to handle bounces at the SMTP server. There are some significant advantages to handling bounces at the SMTP server, rather than waiting to handle them after they are delivered to the POP server. If the POP server or the remote server sending the bounce is busy, a bounce may not arrive for several days and a delay of a day is very common. Since most SMTP servers will also generate a bounce from information gained during the SMTP conversation, you may receive most bounces immediately. The possible actions taken for any bounce format are flexible, since the Bounce Filter in XMS allows for multiple bounce handlers. One may log the bounce information to the database, while another may remove addresses from a list or redirect challenge response bounces to another email address. A handler might even pause or stop a group of messages from being sent and log the uncompleted addresses so that problems can be corrected and the uncompleted messages can be sent again. The same architecture works well for spam complaints, as XMS has the ability to recognize the original recipient for those complaints and remove them from lists.

If you haven't already begun work on handling bounces, you can start easily with a trial version of one of the products mentioned in this article. If you have, you may learn some new things by reviewing the products yourself. Most of us can't simply ignore them any longer.