Return Path: How Engagement Metrics Influence Deliverability

Many senders have noticed changes in the way that ISPs do their filtering, notably at the big four of AOL, Yahoo, Microsoft and Google, and have been scratching their heads as to what changed, and what can they do now to get delivered back to the inbox. The answer is in how ISPs are calculating sender's reputation scores (hint: it's really not that new). Less than savory senders are always looking for ways to game the system to bypass current filtering methods. As a result, ISPs and email providers are constantly changing and improving their filtering methods.

The major email providers are already using, or plan to use, a broad set of engagement metrics to determine inbox placement, not just clicks and opens as has been widely reported, to determine the level of user engagement for different senders. These include
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By Tom Sather Oct 22 2009

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This is really good bit of info. Most of revolved around "don't spam people - if they've asked for it, give it to them, if not leave them alone until they do", which is general permission rules which we should all be running with anyway. He does also suggest a deeper level of profiling per recipient: are they interacting a lot or only on various occasions and if so is there a pattern, if there is email them when you know they will interested. The basics of that is to give people frequency options as part of your preference centre.
Depending on how often you want to email. If you email daily give people the option to a weekly round up, if you email weekly - offer a monthly round up, if you do monthly - offer a quarterly. You can even give people a list of months that they want to receive them, it's all do-able with the right software or ESP.
This was people can get the emails when they need them.

This also ties a little into an old article I wrote on the EMM about how Spam Filters have evolved due to spammers trying to beat them and how to avoid the inconvenience of being mistaken as a spammer.