Note: by external website I mean a website that we do not have access to the code. For example www.facebook.com
I want to record how many social share clicks we have from our customer newsletters. For example, when a customer receives a newsletter they can click "Share this on Facebook" which shares the hosted version of the newsletter.
If I wanted to record these newsletter clicks to our website I understand we'd use Google URL Builder (https://support.google.com/analytics/answer/1033867?hl=en) to create a UTM URL but because we're linking to an external site, how do we record this?