Return Path published their most recent Global Deliverability report this morning (available here - requires registration). It shows that inbox placement of mail has decreased 6% in the second half of 2011. This decrease is the largest decrease Return Path has seen in their years of doing this report.

To be honest, I’m not surprised at the decrease. Filters are getting more sophisticated. This means they’re not relying on simply IP reputation for inbox delivery any longer. IP reputation gets mail through the SMTP transaction, but after that mail is subject to content filters. Those content filters are getting a lot better at sorting out “wanted” from “unwanted” mail.

I’m also hearing a lot of anecdotal reports that bulk folder placements at a couple of large ISPs increased in the first quarter of 2012. This is after the study was finished, and tells me increased bulk folder placement is more likely to be a trend and not a blip.

One of the other interesting things from the study is that the differences are not across all mail streams, but are concentrated in certain streams and they vary across different regions.

Delivery by mail type and region. (APAC: Australia and Asia-Pacific; CALA: Central and Latin America; EMEA: Europe, Middle East and Africa; NOAM: North America and Mexico) Source: Return Path

Just looking at the NOAM region, we see that gaming mails have the worst inbox delivery, but most of the mail is getting through the IP filters. Placement of gaming mails in the spam folder tells me there’s a lot of content based filtering happening. For retail mail we see a different pattern. More mail is missing and less mail is filtered to the spam folder. This indicates a lot of IP based filtering, but if a mail gets past the IP filters, it’s more likely to end up in the inbox.

This chart really does demonstrate that “Best Practices” aren’t global. They’re very dependent on the type of mail and the recipient profile. In North America, too, it shows that mail people interact with regularly is getting to the inbox reasonably consistently. It’s the mail people don’t necessarily care if they get or not that’s suffering the most.

Another interesting data point is how gaming mail changes across various regions. In APAC, gaming mail is hitting the inbox 91% of the time. That may be a consequence of the number of people in Asia employed full time to play games (gold farming) and their interest in receiving mail about work.

Overall, this report tells us that delivery is only getting harder and more complex. Mail isn’t going to the inbox as much as it used to, and that means senders are going to have to keep adapting to recipients wants and needs.