G is for Gladwell...Malcolm Gladwell
Ever read his book Blink – The Power of Thinking without Thinking?
It's a book about rapid cognition, about the kind of thinking that happens in a blink of an eye. When you meet someone for the first time, or walk into a house you are thinking of buying, or read the first few sentences of a book, your mind takes about two seconds to jump to a series of conclusions.
Indeed, it could very well be about when you see an email in your inbox.
What do you see? What makes you decide within that blink of an eye whether to open or delete?
I would suggest that the first two seconds is also influenced by the conversation you have had with that brand...if their content has been relevant then I reckon it gets opened and read. Each 2 seconds has already been influenced by the last time they gave you 2 seconds with your email, on your website, reading your tweet.
First impressions really do count, but remember that each first impression is judged on experience