Email attrition is where a proportion of a list is no longer usable due to the subscriber addresses being invalid. Addresses can become invalid for a number of reasons, such as the subscriber changes jobs, or when a webmail address has been inactive for a long time.

The attrition rates we see vary from list to list. We would expect the attrition on average to be about 15% per annum, but can be higher. For example we’d expect to see a higher bounce rate for first time deployment to a list that had no confirm or double opt in email.

The reasons why emails are junked is a huge subject and is always changing. There are three main categories in understanding deliverability. We briefly look at these three categories, and the key points of each:

1. Infrastructure
   o The set-up of your sender domain and IP address has an impact on delivery. Any issues are usually easily resolved and is part of our normal service.
   o Infrastructure includes (but not limited to) SPF records and domain keys, IP isolation and whitelisting.
2. Content filtering
   o Content may be filtered at several points along the path of an email – by a firewall or spam appliance, by the mail server or at the local inbox.
   o Content filtering varies between ISP’s, corporate mail servers and even individuals.
   o Testing eliminates most content filtering issues and should never be overlooked.
3. Reputation
   o Includes block lists which you can find yourself on if your list contains spam traps or if you exceed a threshold of complaints.
   o ISP’s evaluate subscribers behaviour towards a sender including the ratio of emails that are marked as spam, deleted without being read and whether recipients are even opening your email.

So, our advice? Send relevant, timely emails to subscribers who’ve asked to receive it.