A permission-based email is one sent to someone who has given the sender permission to send them emails at their address. Why does permission matter? Your open rates will remain low if you don't ask for permission. You're not just less likely to earn sales, but you're also more likely to get flagged as spam. What is permission? Permission can be implied (if you've done business with a client before, there's nothing stopping you from contacting them again) or express (through an online sign-up form or other explicit agreement).