You can add a little post-script to the end of your email copy, such as "Not responsible for your company's social media? Feel free to forward this ebook to a friend or colleague using social media marketing." Link the call-to-action to a pre-made email, complete with subject and body text. That way, all someone has to do is enter their associates' email addresses and hit "Send."
Make your offers feel relevant. If you offer people something they don’t think is relevant for them, they also think you don’t know them or understand their situation. Segmenting people based on their interests, problems, company sizes, and other things can help with that a lot. But it’s not enough. Your offer might be a perfect fit for them, but how you present it has to be a fit, too. Focus on describing their problems, how they’ll use the product or service, and what they will have in the end. Don’t talk about it from your perspective. No one really cares what you think about your product as much as they care about what they’ll get from it.
When you're using email as a marketing tool, you're working on a pretty personal basis. This isn't ‘drive-by' stuff -you're directly targeting customers from their inboxes. There's a huge amount of potential which comes with this kind of marketing... but you'll only reap that potential if you REALLY understand both the marketplace you're operating from, and the audience you're talking to.