Is there a way to create a block or element in an email that will be visible to certain people (segments), but not others? Snippets are good for showing different content to different people, but I am wondering if there is a way to hide certain elements depending on who is reading the email.
I mostly use Email Scripting (Velocity) for this. Once you get the hang of it, it's quite powerful in terms of showing/hiding elements or dynamically building emails on a user level.
One message in my current instance has 900+ variations and Velocity builds it out on the fly.
Here's a link to some resources:
Double-tripling down on Mark's recommendation.
Using Velocity allows for hyper-segmentation. You can create infinite content variants, even including segments themselves as criteria.