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.

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Last week ReturnPath published a study that shows 20% of permission based email fails to be delivered to the inbox. For this study, ReturnPath looked at the mail sent by their mailbox monitor customers and counted the number of deliveries to the inbox, the number of deliveries to the bulk folder and the number of emails that were not delivered.
At US ISPs 21% of the permission based emails sent to the ReturnPath probe network did not make it to the inbox. 3% of the emails sent went to the bulk folder and 17% did not make it to the mailbox at all.  MSN/Hotmail and Gmail were the worst ISPs to get mail to. They each failed to deliver more than 20% of the mail that was sent to them. At Canadian ISPs, even less of the mail made it to the inbox, primarily because primus.ca is such a large portion of the Canadian market and they use Postini as a filter. Postini is a quite aggressive filter and takes no feedback from senders.
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There are a lot of reasons an email doesn’t get to the recipient’s inbox or bulk folder. Mail can be hard blocked at the MTA, and rejected by the ISP outright. Mail can be soft blocked at the MTA and the ISP can slow down sending. Sometimes this is enough to cause the sending MTA to stop attempting to deliver the mail, thus causing mail to not show up. Both of these types of blocks are usually visible when looking at the bounce rate.
Some ISPs accept mail but then fail to deliver it to the recipient. Everything on the sender end says the ISP accepted it for delivery but the ISP just drops it on the floor. This is the type of block that a mailbox monitoring program is best able to identify.
Despite all the discussions of numbers, many marketers are still not measuring the variables in their email campaigns. Ken Magill wrote today about a study released by eROI that indicates more than a third of marketers are not doing any testing on their mailings.
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