In this post, Stefan Pollard talks about why subscribers go inactive and how to respond to that. 

He lists 8 main reasons why subscribers stop responding:

1. List age. As e-mail ages as a marketing channel, mailing lists themselves get older. If addresses on your list are five to 10 years old, they could be abandoned but not invalid yet.
2. No welcome program to engage new subscribers immediately.
3. Messages that don’t meet subscriber expectations or match preferences.
4. Weak inbox presence (unbranded sender line and/or generic or boilerplate subject line).
5. Unsubscribe process that’s hard to find, complicated, or untrustworthy.
6. Large percentage of Web e-mail clients, like Yahoo or Gmail, with high mailbox storage capacity, allowing unopened e-mails to pile up.
7. Mailing frequency – either too frequently for subscriber comfort and expectations or too seldom.
8. Offer repetition, where you rotate through the same offers every week. Subscribers catch on and simply ignore your messages, waiting until they are finally in the mood to purchase.

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