Let me write up the professional version the way only I can.

Start with the formula described in the article but call rather than send an email.

Call them again 12 or 24 months later.

The script should be in your own words: Some people you need to talk to or see every day, some every week, some every month and some people every few years. Don't worry about it, I'm not going to stalk you. I will call you again in two or three years.

Then talk like coworkers about new jobs, earnings, the good the bad and the ugly, learn they got married/divorced, had kids, left the country for a while. etc etc

Keep the call under 4 minutes. Some people don't know how to terminate a phone call.

After each phone call send them an email summarizing the things you've talked about. Include the previous email.

You will find that, provided there is no obligation to stay in touch, people don't mind telling what they did over the last two years. Even if they don't like you. The fact that you've asked puts you well ahead of most people they know.

The 3rd call after 3-6 years is simply hilarious. They know the drill, the conversation can be as short as two minutes. Thanks for your time, we should do this again in two years!

You methodically hammer out the email again and go on with life.