- Unsolicited - Unknown Source: Spam, pure and simple. You delete it quickly and are probably more than a bit annoyed.
Unsolicited - Known Source: You may know the company, but you still didn't request it. Still annoyed, perhaps slightly less so depending on your existing opinion of the company. However, your opinion probably went down slightly after receiving their spam.
Opt-In - Coerced: An email received from a company who required you to give them your email address in order to get to something you wanted (a free white paper, etc.). In reality, you really don't care to hear from these folks again. Most likely you'll delete it, or perhaps open .5% - 1% of the time when you're cleaning out your Hotmail. If you have the energy and time, you'll probably opt out (although most people don't, preferring instead to ignore it or flag it as junkmail that gets routed to the delete folder).
Opt-In - Desired: This is actually becoming less common and less needed with RSS, but there are times when you actually do want something sent to you on a regular basis. Sometimes it's related to offers, most often it's related to valued information. These emails get opened, but still only 3% - 20% of the time.
Forwarded From an Annoying Friend/Colleague: You know the ones, thinking every other joke or urban legend is worth forwarding to their entire address book. You may pay attention for a split second, but mostly just to shake your head and wonder why they have so much time on their hands. These are tougher to opt out of receiving, but mentally you're most definitely opted out.
Forwarded from a Trusted Friend/Colleague: Ah, now we have something. This is an email from someone who you know personally, or have placed some trust in because of others' opinions of them. You've experienced a track record of value in what they send, so most likely you open it. You may even forgive them a couple of times if they send something less than valuable, but the long-term trust remains. These are the pinnacles of influence in a word-of-web world.
The question is: Why do we plan and spend so much time and money on architecting "campaigns" that look so much like the first few scenarios, and so little on thinking of something uniquely and consistently valuable that it would earn a forward from a trusted source?
Sure, it's harder. And we're not at a point where marketers can completely rely on word-of-web to generate enough response volume. The scale just isn't there. But...If we re-prioritized our planning, if we started with that end in mind, wouldn't even the rest of our "traditional" marketing (including traditional digital marketing) be that much more effective?
If we started with "sticky" in mind, most likely it would stick to all of our communications and lead us towards higher return on marketing investment.