... for goodness sake, if you're going to email somebody a plug, DO NOT apologize for it! It just makes you sound wimpish and inexperienced and kinda stalker-ish. Yes, stalker-ish, because then it doesn't sound like a business letter anymore. If you want to plug something in a direct email to somebody, be confident about it. Sell it to them. Think along the lines of a query letter. Connect with the person you are emailing and tell them why you think they, specifically, would be interested in your work.
Forget about your insecurities. If there is any place you can disguise low self-esteem, it's via email. If you really really want to plug something to an individual via an email, you really really need to take advantage of that.
Anyhoo, that's my thought of the day. I like to respond to all the plugs I receive, despite how they're written, but someone else might not.
What do you think when you receive a plug for something from someone you don't know from a bar of soap? Do you read them? Do you cringe? Do you not even bother and delete them? Do you respond to some and not others? Why? What is it about the ones you read that sparks your interest?