Delay-based filtering is primarily used to:

Delay-based filtering is primarily used to insert a pause to detect spam mail. This technique involves delaying the processing of incoming email to assess various criteria and potential indicators of spam. By implementing a short delay, the system can gather more information about the email's origin, behavior, and any associated sending patterns.

This method helps to filter out spam by analyzing responses from recipient servers or monitoring subsequent interactions that may indicate whether the email is legitimate or not. It provides an additional layer of assurance and screening against unwanted or malicious content, which is crucial in maintaining the security and integrity of email communication.

In contrast, analyzing email content, verifying sender's address authenticity, and rejecting email based on size are different strategies that focus on other aspects of email filtering and do not rely specifically on timing or delay mechanisms.