Our Knowledge Base contains 1000+ pages of information, and is a great place to start getting answers about using Mimecast products. Just search for a keyword or phrase or click a … Nov 15, 2019 · With all rejections, Mimecast sends a rejection code to the sending mail server, and the mail server should forward a Non-Delivery Report (NDR) to the sender. See the "Common Rejection Types and Resolutions" section of the Message Center: Rejected and …