Email Open Rate Metrics

I am always asked about this and there is always a swirl of confusion.

Email open rates are not an exact measure.

I just read a very good summary of the problem on the Marketing Sherpa blog.

The Annoying Imprecision of Email Open Rate Metrics

There is some good information in the comments too.

One thing i do agree with and tell clients all the time is that your open rate should be looked at over time. You can see trends and pick up problems there.