# engagement

- [What is a preference center?](/explained/engagement/what-is-a-preference-center)
- [What is click-through rate for email and SMS?](/explained/engagement/what-is-click-through-rate)
- [What is CPaaS?](/explained/engagement/what-is-cpaas)
- [What is omnichannel vs multichannel messaging?](/explained/engagement/what-is-omnichannel-vs-multichannel)
- [What is open rate, and is it still a useful metric?](/explained/engagement/what-is-open-rate)
- [What is unsubscribe rate, and what is normal?](/explained/engagement/what-is-unsubscribe-rate)