Explanation
Email-to-case is a channel that meets the requirements of logging the case thread and storing attachments to the case record. Email-to-case is a feature that allows you to automatically create cases from incoming emails sent to your company's support addresses. Email-to-case preserves email formatting and supports HTML emails with embedded images. Email-to-case also captures email attachments and adds them to the case record. Email-to-case tracks the entire email conversation between the customer and the agent, and logs it as a case thread on the case feed or case comments. Verified References: Service Cloud Consultant Certification Guide & Tips, Email-to-Case Overview

Explanation
Appointment Assistant is a feature that can improve the customer experience by reducing the 4-hour long appointment windows and providing information about the technician's arrival time. Appointment Assistant is a feature that allows customers to track the status and location of their service appointments in real time through SMS messages or a web page. Appointment Assistant can help customers plan their day, reduce no-shows, and increase satisfaction. Verified References: :
https://help.salesforce.com/s/articleView?id=sf.field_service_appointment_assistant_overview.htm&type=5 :
https://help.salesforce.com/s/articleView?id=sf.field_service_appointment_assistant_setup.htm&type=5