- * The Received: header is special. We concatenate all
- * instances of the header as we use this when analyzing the
- * path the mail has taken from sender to recipient.
+ * The Received: header is special. We concatenate all instances of the
+ * header as we use this when analyzing the path the mail has taken
+ * from sender to recipient.
+ *
+ * Similarly, multiple instances of Delivered-To may be present. We
+ * concatenate them so the one with highest priority may be picked (eg.
+ * primary_email before other_email).