The easiest way to send people from an email to your YouTube video is to make the email all about the video's main benefit or a really juicy part of it. You should use a strong headline that makes them curious about what is in the video, maybe even use a nice picture or a GIF from the video to grab their eye. Then, have one big, clear button or link that just says something like "Watch the Full Video Here" so there is no confusion about where to go next. Keeping the email very short and focused on that single action works best. How often do you think sending an email that only has one goal, like watching a video, works better than sending a longer one with many links?