Message Queuing & Segregation: Lessons from the Airline Industry

Note: This also appears at http://www.messagesystems.com/wordpress/?p=38.

Many email marketers are unaware of the importance of message queuing to the successful delivery of their email. As a component of their messaging infrastructure, queuing is something that marketers typically defer to their IT department to manage. Yet, the reality is that queuing and the segregation of message streams can make the critical difference between the success and failure of a company’s messaging programs, and therefore, should be of concern to both the IT and marketing departments.

Effective queuing really comes down to the choice of messaging infrastructure. When using a technologically advanced messaging platform, companies can efficiently manage parallel queues with messages assigned into multiple streams to ensure that each stream flows at an appropriate rate, providing efficient delivery of all classes of traffic. Unfortunately, those that rely legacy MTAs have no such options. They’re left trying to manage the bottlenecks and slowdowns that result from poor architecture with complicated priority schemes within a single queue.

Recently, one legacy MTA provider suggested that their routine for queue prioritization was the answer for reaching high-value customers first. While the business need is certainly legitimate, trying to prioritize messages within a single queue is both outmoded and a solution to a problem that should not exist in the first place. There are better ways to satisfy this need that are both simpler and more powerful at the same time. To illustrate my point, allow me to provide an analogy that should be familiar to my fellow business travelers.

One of the most common headaches for the air traveler is the security checkpoint; you get your ID checked, get in line, get your ID checked again, get in another line, empty your bags, take off your shoes and belt, get in yet another line and then get radiated in the name of public safety. During the highest traffic times these lines can become so long that people start missing their flights because there are a very limited number of security checkpoints and the airports were architected in a time that predated the need for such extensive security. This fundamental flaw in the architecture of the airports means that the current needs of travelers for additional parallel security screening checkpoints cannot be met, and everyone has to wait in a queue to get to their plane, sometimes with unacceptable results, leading to additional costs for all involved and potential lost business.

This is handled in a variety of ways, including performing the security check at every gate area (creating a very parallel security screening system) and by using priority security lines. Imagine for a moment that instead of this solution, the airport chose instead to assign priority on an individual basis to every single passenger and then tried to sort the individual travelers in the security line. As you can imagine such a solution would require additional work to make the individual assignments and then keep track of who ranks where in the line, with a risk that low-priority passengers would find themselves significantly delayed as they were repeatedly bumped. In all my travels I have never seen such an approach, primarily because the airports already have an approach that works.

Find a particularly efficient airport and what you’ll see is a fairly consistent set of practices:

  • Separation of passengers into queues based on their fitting into a certain profile.
  • A large number of parallel checkpoints.
  • Efficient handling of passengers.
  • Intelligent queue management that can modify queuing on the fly to meet circumstances.

Look at a particularly efficient airport and you will see multiple queues, including queues for:

  • Frequent / First Class travelers – The most frequent travelers and those who sit in First Class. These people bring a lot of value to the airlines and receive a lot of value in return.
  • Expert travelers – A new lane starting to appear in some airports, for those who are experienced in getting through security and unlikely to cause delays.
  • Family / Special Assistance – A slow lane, these groups will take longer to get through security.
  • Casual Travelers – A lane for those who move at an average speed through security.
  • Staff / Crew – While in some airports workers and air crew jump to the front of the line, the most efficient airports avoid this disruption by maintaining a separate checkpoint for those who work at the airport, minimizing disruption and ensuring that staff can get to work on time.
  • Specialty – From time to time I’ve seen the airport create a special temporary queue for unique groups such as chartered planes by opening a checkpoint and redirecting the group to the specialty group.

Not only has the separation of travelers into queues according to their profiles (including their priority as a group) proven sufficient to make prioritization by individual traveler unnecessary, it is much easier to manage.

While separating passengers into a number of queues can certainly benefit airports, the most efficient airports are also architected to operate a large number of parallel checkpoints, preventing a situation where every passenger in the airport needs to be funneled through the same metal detector. Imagine an airport trying to service millions of passengers a year on only one or two metal detectors and a single x-ray machine.

In addition to having many checkpoints, the best airports will also have efficient checkpoints, maximizing the flow of passengers through any given checkpoint through better design of the checkpoints and better training of the staff, all without compromising safety.

Perhaps most importantly to the smooth operation of an airport is intelligent management. I’ve seen airports where there were several queues open but empty because the people managing things weren’t flexible enough to reassign lines and adjust the queues to ensure well balanced passenger flow. The best airports will change the designation of queues, move staff around and even redirect passengers to alternate checkpoints that are less busy, all in the interests of moving the highest number of passengers per hour.

Senders can follow these same principles to get maximum throughput and deliverability in their own environment:

  • Segment mail by profile.
  • Choose a sending solution that supports highly parallel sending.
  • Choose a sending solution that provides sufficient throughput.
  • Choose a sending solution that is intelligent.

When sending, remember that segmentation is not just for who to send to or what to send them, but for deciding how to send a message and with what priority. You will want to create queues for high priority messages to satisfy your most valuable customers, queues for high-reputation traffic that delivers without issues as well as for traffic that you expect to deliver slowly (one example is traffic that results in human interactions, you may need to slow this to prevent overloading your call centers), test and administrative traffic that needs to go out as soon as possible and transactional traffic that should not queue up behind bulk sends. This is a common practice among ESPs, who often add specialized segmenting for scenarios such as new customers and customers with specific SLAs.

As with the airports, you need to architect your environment to be able to handle more traffic in parallel. This can be accomplished by adding more injectors and more messaging infrastructure, or by adding better infrastructure. Look at your existing solution: how many IPs can it send from? How many messages per hour can you send on a single machine and how many concurrent connections can it handle? Most Open Source solutions can handle one IP address, send 100,000 messages per hour at most, and can open less than one hundred connections. Low-end commercial solutions can often do over a hundred IPs, send close to a million messages per hour and can handle a few hundred to a couple of thousand connections. On the high end you have carrier-grade systems designed for the enterprise such as Momentum by Message Systems, which can utilize thousands of IPs to send millions of messages per hour across tens of thousands of concurrent connections (while you will never open more than a few connections to a given ISP on a given IP address, lesser solutions will fall short when sending across hundreds of IPs to thousands of ISPs, defaulting to ISP prioritization as a workaround).

Finally consider the intelligence of your infrastructure:

  • Can your infrastructure send across all servers simultaneously and fail-over in the event of an outage?
  • Can your infrastructure adjust throttles on the fly based on responses from the ISPs and bounce and feedback loop data?
  • Does your infrastructure handle queues so efficiently that performance is the same with thousands of messages in the queues as it is with millions of messages in the queues?
  • Can your infrastructure dynamically change from email to other protocols such as SMS and MMS based on subscriber preferences and ISP responses?

If not, we should talk.

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