Details
Conditional Content allows you to display only the content of interest to your contacts, depending on data that they have listed against their contact record.
Conditional Content in an Email
Conditional Content can be enabled on most components in an email, with a limit of 5 conditions per component (excluding a 'default' option, which is what will show when none of the other conditions are met).
Each email can have up to 75 components with conditions - however, you will receive a warning if your email has more than 50 conditional content check. If your email has more than 75, you'll need to reduce this number (by removing some of them) before being able to save your message.