There are so many bounce codes used by the various ISPs and receivers that it’s hard to keep them all straight.

Now there is a great resource for most of the known bounce codes to help simplify your tracking and processing. The eec’s Deliverability Roundtable has put together a repository of common and available bounce strings senders might see from current ISPs (email receivers).

The forum is setup on Get Satisfaction as a dynamic and interactive site that allows users to request information and update bounce strings as they change. The ISP serving the bounce, the bounce string text and next steps for a sender are written out by bounce code here.

http://www.getsatisfaction.com/deliverability/tags/bounce_codes

According to a Return Path’s latest Deliverability Benchmark Report, of the 21% of email that is not delivered to the inbox, only 3.3% is sent to a “junk mail” folder and 17.4% is not delivered at all – it just vanishes!

Return Path did not state where they believe the email to be, but we suspect that it is floating in deep space, possibly captured in the crystal prison of the three Krypton prisoners from Superman.

Some other notable points from the study:

• It is easier to deliver to US ISPs than Canadian ISPs. Inbox placements of mail sent to US ISPs was 82% in contrast to 75% sent to Canadian ISPs.
• B2B delivery rates are less than that of B2C email 72% vs 79%. This is in strong opposition to what has normally believed to be the case. Accounting for this is the fact that businesses are being protected by ever advancing systems like Postini, Synamtec and MessageLabs.
• In the US, Gmail is the hardest ISP to penetrate and Cox is the easiest.
• In Canada, Primus.ca was the hardest ISP to penetrate and Telus was the easiest.

I encourage you to download the full study, which is brief but very informative, and includes colorful charts and graphs:

Return Path Deliverability Benchmark Report

We built an auto-responder that can be used to test your bounce and feedback loop processing systems. Feel free to use it for your testing purposes.

fbl-test@service.socketlabs.com
Auto responds to From address with a feedback loop report in ARF format.

bounce-test@service.socketlabs.com
Auto responds to the Return-Path with a bounce message.

As a side note, the autoresponder was built using the .Net API in Hurricane MTA Server.