Your marking emails might not have a one-click unsubscribe link but Gmail certainly has a one click spam button.
Two ways you can keep me as a subscriber:
1. Remind me what the hell it is your company does/sells in the first sentence. Between my signup and now, chances are about 95% that I forgot what I even signed up for.
2. Make it easy to unsubscribe. That means a very visible one-click link. Unsubscribing doesn't mean I'm no longer interested in your product. But making it difficult to unsubscribe says a lot about how I will be treated as your customer.
<extra> Go easy on the HTML / CSS / Images. </credit>
@easternmonk: That's the thing -- I did mark them as spam in GMail. I assumed it would block future emails from Linked-in but not the case. ... Somehow they continued to come in.
@sehugg: That too! I complained about their this on Facebook and I had friends (yes, plural) who had deleted their account because of the spam and yet were still receiving it. Unbelievable