Anyone who’s waited tables knows it forever changes how you experience service as a customer. You become a better tipper—but also a tougher judge of performance. Working in marketing, as it turns out, can have quite the same effect.

About a week ago, I got an email from my children’s orthodontist. We go way back. My son went through his “joy of braces” phase long ago, and now my daughter is finally wrapping up hers. The email was an automatic reminder about her automatically scheduled appointment. However, my daughter had just gone away to college, so the appointment would have to be rescheduled.

Here’s the thing. The email included no instruction for disconfirming or rescheduling this appointment, so I did what seemed most natural. I sent a reply. But after several days without response, I broke down and called to follow up. The receptionist explained, “Oh, we don’t get those emails back. It’s all automatic.”

I felt like I was taking crazy pills. Why on earth would a business reach directly out to a customer then ignore the direct response they get? Two-way email is not rocket science.

Far too often, I see this kind of mistake in business communications. If you send a question in email, calling up later to ask, “Did you get my email?” may come off as inconsiderate, especially if you’ve failed to notice your audience already took the time to write you back.

Different media are good for different kinds of communications. Whether you’re reaching out by email, tweet, telegraph or smoke signal, my advice is to stay on the same channel and see it through, unless you specifically signal a jump to another channel. Otherwise you risk your audience’s good will by double-dipping into their valuable time.