When I work with business owners, they frequently resist removing inactive subscribers... they know that person still exists. Sadly, being alive doesn't make you a reader or user of email. And more seriously, inbox providers are driven to eliminate unwanted messages. If you manage an emailing list you have to get ahead of the problem and take inactive subscribers off. To have a healthy relationship with our customers, we have to learn their communication preferences and respect them.
Sailthru: Why Using Email Engagement Suppressions Works for Inbox Placement, so-called evergreen content with no date, by Nancy Harris
As users open, read and delete messages, Gmail is watching. They’re curious how long people spend reading messages and which ones they forward on or reply to. On the negative side, they’re also interested in which messages people move to different folders or mark as Spam. ISPs, especially Gmail, are looking to make their users happy. As a result, they deliver mail that they see their users engaging with.
However, Email Service Providers (ESPs) don’t have access to the same metrics. For companies like Sailthru, opens and clicks are the best indicator of an inboxing issue. Targeting users who have been engaging with the mail stream helps to maintain healthy inboxing or mitigate any inboxing issues.
It helps to suppress those people who aren’t engaging, at least for a certain period of time. Not opening or reading messages, those users are dead wood.