I recently read an article explaining how people are much more satisfied with wrong results if they understand how the results were reached than wrong results from a process they don’t understand. If we assume even a modest 5% false positive with Philip’s suggestion, it might create more frustration than twice as many false positives in something I understand (i.e., just using the subject line).

On the other hand, it might simply be the easy thing to do from an engineering perspective. I’d imagine the subject line is pretty well indexed in any email client, so it should be relatively simple to correlate when organizing thousands of messages for a view (not everybody subscribes to zero inbox after all).

I recently read an article explaining how people are much more satisfied with wrong results if they understand how the results were reached than wrong results from a process they don’t understand. If we assume even a modest 5% false positive with Philip’s suggestion, it might create more frustration than twice as many false positives in something I understand (i.e., just using the subject line).

On the other hand, it might simply be the easy thing to do from an engineering perspective. I’d imagine the subject line is pretty well indexed in any email client, so it should be relatively simple to correlate when organizing thousands of messages for a view (not everybody subscribes to zero inbox after all).

There is actually a standard header for this (“In-Reply-To” — for example, “In-Reply-To: “).

Unfortunately not every mailer in the world adds this header so mail application developers try to get fancy. Like so many other design choices, Apple always shoot for fancy over basic.