It seems so 20th Century. With text messages, Facebook messages, tweets, video chat and now Ello--not to mention good, old-fashioned email--why would anyone use U.S. postal mail to reach out to customers?

Because, depending what you're trying to accomplish, it can be surprisingly effective, according to small-business marketing maven Mark Satterfield, author of The One Week Marketing Plan. Let's start with the response rate for unsolicited messages. "Direct mail responses vary, but anything from 0.5 to 2 percent is considered good," Satterfield says. "For unsolicited email marketing, a good response rate is 0.01 percent." Not only that, research shows that physical media, such as a paper letter, postcard or flyer, leaves a greater impression on the brain than electronic media does. "So you have a higher chance that your promotion will be acted on."

There's also a higher chance it will stand out from the crowd. "Even in consumer marketing, the volume of mail people receive every day has dropped dramatically," Satterfield says. "So we're seeing even an oversized postcard with an intriguing call to action having very good responses."

With all these advantages, it's worth considering a direct mail campaign any time you're looking to increase sales or find new customers. But Satterfield says there are certain situations where direct mail is particularly effective:

1. When you want to reach high-level decision makers.

Email marketing to this demographic never works, Satterfield says. "Their spam filters are so tight that if you send unsolicited email it has zero chance of getting through," he says. "Whereas if you send a direct mail piece that looks like business correspondence, it's much more likely to get through."

2. When you're introducing yourself.

New to the neighborhood, or the industry? A direct mail piece is a great way to grab people's attention in a crowded marketplace. An oversized postcard with compelling graphics might just catch their eye when an online ad or unsolicited email would be ignored.

3. When you really want to target your audience.

One nice thing about buying direct mail lists is that they can be targeted quite precisely. "If you want to target people by zip code or profession or which associations they belong to, you can buy all those lists," Satterfield says. If you've imagined personas for your target customers--and if you haven't you should--you can create direct mail campaigns targeted tightly to those people.

That can help you save on costs as well. If tight targeting has produced a list of only 100 people who truly fit your target customer profile, and your direct mail item costs $0.65 apiece, you can reach that target market for only $65 plus the cost of buying the list.

4. When you're tying a promotion to a holiday or event.

Direct mail is an especially way to get the word out and customers through the door when you're running a promotion that ties in with an event such as a sporting match or a holiday. "If you tie your services or product to a holiday and then do promotion around that holiday, it can be particularly effective," Satterfield says.

"We had an irrigation service client who did a direct mail piece around Arbor Day," he adds. "Who even remembers when Arbor Day is? They sent an oversized postcard reminding people about the holiday and offered a discount. They sent it to a zip code where there were expensive homes. It was very successful."

5. When it sends people to your website.

"Direct mail is a great way to get people's attention and start a relationship," Satterfield says. "It's not that effective at actually selling things."

This is why your direct mail marketing should have a strong call to action, which in most cases will be to send people to your website for more information, to receive a discount, or download a free piece of content.

One consulting firm had a free report available on its website and the purpose of the direct mail piece was to get recipients to download the report. But to do that they had give their names and they were offered the chance to opt in for email messages. Opt-in email lists are very effective for marketing, so the combination of the direct mail piece and the website were very effective, Satterfield says.

"If you view the objective of your direct mail campaign as getting people to express interest in you, then it's very powerful," he adds.