The Message Bus Blog

Being able to track email open rates is an important tool to have available when seeking to optimize message deliverability. Message Bus has recently incorporated open rate tracking into its product offering. We thought we’d take this opportunity to share how this important functionality works.

In a nutshell, open rate tracking involves counting server requests. When open rate tracking is activated, Message Bus inserts an HTML image tag into outbound message bodies. As recipients open their mail, their email software calls back to the Message Bus servers to retrieve the image. Message Bus intercepts the image request, records its occurrence, and then returns the image (a transparent one-pixel-square gif file).

Obtaining an accurate count of email open rates is a hard problem to solve. Once transmitted, messages are no longer directly observable by the sending servers. Keeping track of open rates thus requires the use of methods which reliably cause message recipient’s email software to ‘phone home’, calling back to the sender’s servers in some fashion so as to be counted. The problem is complicated by the fact that modern email clients are constructed so as to prevent messages from ‘phoning home’ by default (as a spam prevention tactic). The HTML image method implemented by Message Bus results in the most accurate and reliable open rate count possible under the circumstances.

By default, HTML image requests inserted into customer’s outbound emails call back to a domain dedicated to this counting purpose: ‘services.messagebus.com’. Clients may optionally override ‘services.messagebus.com’ with a custom domain of their choosing (e.g., ‘services.yourdomain.com’) so as to remove any references to Message Bus within their message bodies.

As a result of the system issues described, open rates are imperfect and imprecise but they serve as a means for triangulating on deliverability.  We look forward to working with you on improving your email performance across the board.