Direct mail (DM for short) addressed to our company piles up on my desk practically every day.
Given my line of work, I love looking at advertising, so I read as much of that direct mail as I can. It's not that I want to buy the products or services being advertised — I have no intention of purchasing. I'm simply interested in seeing what kind of approach this piece of mail is taking with me as a prospect (laughs).

That said, with daily work to attend to, I don't open and read every single piece of direct mail.
I sort through the DM mixed in with invoices and other mail I need for business.

* DM I want to read right now
* DM I want to read later
* DM not worth reading

This sorting happens almost unconsciously — and in an instant.
What happens to the DM judged "not worth reading"? Straight into the bin, unopened.

Even the DM that isn't worth reading surely had just as much cost and effort put into it as the rest... so what makes the difference?
I think it comes down to whether or not the envelope itself has something that makes you think "I want to open this" or "I have to open this."

The simplest example is an invoice. Envelopes containing invoices addressed to me or the company always have "Invoice" printed or stamped on them.
Seeing that, you judge, "This is something I need."

It's the same with direct mail. Unlike an invoice, the criteria for judging something "necessary" vary widely, but unless there's at least something that makes you feel "this is a message sent to address my own desires or needs," you won't feel inclined to open it.
In other words, the key is whether the envelope itself gives a reason why it "should be opened."

Conversely, when you're the one sending the DM, you have to pay attention to the question, "What is needed to get this piece of mail opened?"
We help clients mainly in the Hamamatsu–Kakegawa area create their direct mail, and one thing that tends to be overlooked is the "envelope."
When a client asks us to create DM, our production staff work hard to devise ways to generate a response — but we make a point of never forgetting to think just as hard about whether we've built in devices that get the mail opened.