Should you always address your mail to an individual at a company? For personal letters, yes. For mass mailings, sometimes yes and sometimes no. It all depends on how good your list is, and who you're really trying to reach.
If you are mailing to your own in-house list, and you're relatively sure the list is up-to-date, then the person on your list is probably still with the company. But if your list has some whiskers on it, there's a good chance the person you're mailing to has either moved up or on. Your mail will either be returned, tossed, or if you're lucky, forwarded on to the replacement. But your mail will be perceived as an insult to the new recipient (why don't you know about me yet?).
Let's face it, if you know the person you're sending information to, it would be an insult to just address it to his or her title. Whenever possible, mail to a person. But let's assume you've bought or rented a list and you don't know everyone on the list. The person you're mailing to may not have decision-making power for your services. If the person you've mailed to has moved on to a new position, the new person may see the old name and automatically trash the mail, or the mail room may send the piece back with those wonderful words "NO LONGER AT THIS LOCATION" stamped on the front. And if you've misspelled the name in any way, you create a negative first impression, which is the last thing you want to do with a mailing piece.
If you replace the unknown person's name with a known position or title, you stand a better chance of the mailing piece actually ending up on the right person's desk. Addressing the mail to "Office of the President" or "Secretary to the President" will almost always reach the right person's desk. Addressing mail to the "Office Supplies Buyer" will be directed to the person everyone in the office always goes to when they run out of supplies. It's a good bet that person is the office supplies buyer, even if their actual title is Comptroller or President or even "Lowest Person on the Totem Pole". Addressing a restaurant's lunch menu to "Hungriest Person in the Office" will (a) get a chuckle from the mail sorter and (b) be delivered, most probably, to the hungriest person in the office. More importantly, your mail will be remembered, delivered and read.
Two years ago I prepared a mailing for an air conditioning maintenance company. We addressed the mail to "Person in Charge of Keeping Cool in Summer". Our goal was to reach the person responsible for maintenance problems, whether it was the president or the billing clerk. My client got such a wonderful response he had to stop the mailing after four months because he couldn't handle all the phone calls.
When using a title, your objective is to get to the right person. Simply mailing to a general manager will most likely get to the highest level manager known to the in-house mail sorter (usually the receptionist or mail room clerk). When deciding how to address your mailing piece, imagine you're the desired reader, and then imagine you're the mail sorter. Your goal is not always to impress with a fancy envelope, but to get your mail directed to the right person. Think of the best way to reach that end result. Below are a couple of examples ...
Head Honcho at ... (when aiming for the president)
Chief Cook and Bottlewasher ... (will work equally well for small company presidents and mail directed to housewives)
The Boss at ... (same connotation as Head Honcho)
Computer Expert at ... (will land on the desk that everyone else heads to when the computer doesn't work right)
The list can go on and on. To summarize, mail to an individual's name when you're pretty sure that person is still with the company. But if you're not sure, a creative title can work just as well. Don't be afraid to break the formal rules of addressing business mail. Your objective is to get noticed and make a sale.