Jeff Parker wrote a "braintrust" essay in my book entitled, Life is a sales call. I believe sales skills map very well to life in general. Working a phone or making in-person pitches teaches numerous lessons. Most notably, in my experience, is that someone may not return your call the first, second, third, or fourth time, but the fifth time you call it happens that they are, in fact, quite interested in your product.
The lesson is basic, but like so many "basic" life lessons, hard to absorb if not learned first-hand: be persistent and keep following up until you hear a definitive "no" (and then just follow up less frequently).
The past few weeks I’ve talked different people who are trying to obtain information / move something forward. I ask, "Did you call Jane?" The answer, "Yep, I called, haven’t heard back." Remarkably, when I probe, they’ve concluded that one non-callback means non-interest.
The same goes with email. Be persistent. Follow up every few days, try different approaches, change your messaging. My sense is if you only followed up once, you probably didn’t care much about the interaction anyway, and if that’s the case, why try in the first place?
Related Post: Two Quick Stories About Persistence