What is one of the features of Email-to-Case regarding follow-up emails?

The feature of Email-to-Case that involves follow-up emails is that they will update the case comments. When a customer replies to an email related to a specific case, Salesforce is designed to automatically associate that reply with the original case. This means that the content of the follow-up email is added to the case comments section, allowing support agents to have a complete view of the ongoing correspondence with the customer within the context of that case. This automatic linking helps maintain the continuity of communication and ensures that all relevant information is captured without requiring manual intervention. It streamlines the support process and makes it easier for agents to track customer interactions.

The other options do not accurately reflect how follow-up emails are processed in Email-to-Case. Follow-up emails are not deleted after a set period, nor are they stored separately from main case records; instead, they become part of the case history. Additionally, there's no requirement for follow-up emails to be manually attached to the case since the system facilitates this integration automatically.