When a corporation sends mail to a person, it's almost always because they want money from the person. Sometimes the person has contracted with the company, and the topic is billing, collections, or account maintenance. (Or even, heaven forbid, a product.) These usually come in plain #9 or #10 envelopes. Because of privacy laws, they usually don't have a lot written on the outside.
More often these days, the company sending mail is just trying to drum up additional business from the person. Anybody who's opened a lot of junk mail has learned how to tell when something is a solicitation. Happy colors, large boldface print, non-standard sized envelopes, and numbers (i.e. a price or interest rate) on the outside are all good indicators.
Every once in a while, a company tries to "get one through the spam filters" by putting a solicitation inside a plain envelope. Verizon Online, I'm talking about you. I do have an account with Verizon, so when I see a plain envelope saying "IMPORTANT INFORMATION ABOUT YOUR ACCOUNT" on the outside, I kinda have to open it. It might actually be what it says. But of course, it's the same solicitation for DSL that they've been sending me twice a month since I cancelled. I'm sorry for all of the actual Verizon DSL customers that have to pay for this. It comes always in full color, often on glossy oversized paper with printing bleeds. They must cost a dollar a piece to send, and believe it or not, I'm not interested in a slow internet hookup that drops carrier every time there is a thunderstorm in the Western Hemisphere.
It's wasteful for a second reason as well: sending me a solicitation in an envelope claiming to contain account information just pisses me off. I guess the purpose is to make me want to become a Verizon customer in another way, but it has the exact opposite effect. I have this image of Verizon Online (Verizon DSL?) as a poorly-managed, money-wasting marketing machine. If it was the only megabit+ internet service available, I might consider it, but as long as there is even one alternative, forget it. Until then, believe me, I know DSL is an option. Verizon, you don't have to keep wasting your customers' money on reminding me about it. How about giving them better customer service instead.