Six months or out

Mickey Chandler has a great post up about Triage vs. Planning. Where he talks about the decisions you make differ depending on the context.
It’s a good read, and I strongly encourage everyone to go give it a look.
But his post led me to a post by Andrew Kordek at Trendline where he claims that there is an industry rule of thumb that says 6 months is the rule of thumb to define an inactive.
Wait, What?
I know there’s a huge amount of controversy in the email space about whether or not you should purge inactive addresses. I know there are some very vocal people who think that removing inactive addresses is tantamount to marketing suicide. But where did 6 months come from? Who made it an industry standard?
If we don’t know where the standard came from, if we don’t know why we’re doing it then what kind of mickey mouse industry are we running here?
There is a lot about email marketing that is empirical. You poke the black box on one side and see what happens on the other. The problem with that is, that we can “discover” a lot of effects that aren’t real, but somehow turn into “you must do this!”
I have no doubt there are times when a 6 month expiry is a good idea. A number of my clients over the last few years use a much, much shorter time because that’s what works for them. I also know there are times when longer expiry times are a good idea, too.
It’s really important that when you’re making decisions about your email marketing program that you don’t mindlessly apply “standards” to what you’re doing. Think about the practical effects of your decisions and put them in context with your overall business plan.
To do otherwise is to kneecap your email marketing program.