Failed delivery of permission based email

A few weeks ago, ReturnPath published a study showing that 20% of permission based email was blocked. I previously discussed the definition of permission based email and that not all the mail described as permission based is actually sent with the permission of the recipient. However, I only consider this a small fraction of the mail RP is measuring, somewhere in the 3 – 5% range. What happens with the other 17 – 15% of that mail? Why is it being blocked?
There are 3 primary things I see that cause asked for and wanted email to be blocked.

• technical issues
• content
• expectation disconnect leading to user complaints

The technical issues range from actual RFC violating practices to minor nits that makes mail look more like spam than legit mail. The software vendors are getting better and I find less and less problems with the header content in emails. The one exception is some of the websites using Java to generate mail based on user activity. Some of the Java mail classes generate very poor headers which can decrease delivery.
Looking beyond the headers, there are still problems in the body of the email. Base64 encoding plain text, either in the subject line or in the body of the email, has been used by spammers to avoid filtering. Some legitimate mailers use software that base64 encodes plain text email, causing delivery problems. Invalid HTML is also a common mistake that can drastically hurt delivery.
Once senders have confirmed they’re sending correctly formatted, non-RFC violating email, the next big thing to look at is the content of the email. I’m not talking about the number of exclamation points in the subject line, or the word “free” or “unsubscribe” or content like that. I’m talking about more fundamental content. Is the sender selling loans, stocks or male enhancement products? If so, they are going to have delivery issues no matter how good their opt-in process is. Advertising heavily spammed or phished domains, like links to Amazon.com or eBay.com can also decrease delivery of wanted email. Some companies hire lots of different senders to advertise their domain. If they hire LegitMailer.com and they also hire spammers, LegitMailer.com will often see delivery problems based on the content of their mail being found in spam.
When this happens there isn’t much that the sender can do other than avoid the problematic content. I have one client who sends opt-in mail but will occasionally see their mail bulk foldered at major ISPs. Typically this is a one day event, and every time I’ve asked the ISPs they have always blamed the content. The companies my customer is recommending in their mail are also being mentioned in spam and so my customer’s delivery suffers.
Finally, there is sometimes a disconnect between what the recipient thought they were opting into and what the sender actually sends. This can lower a sender’s reputation and delivery. The fixes for this are not as simple as making a few technical fixes or changing the content of the email. This is a longer process and requires more analysis of recipients, what they want and how the sender can meet the recipient’s needs.