System 2.0.0.0 4.0.0.0 System.Enum You can use this enumeration to set the priority header of an email message. Specifies the priority of a . Field 2.0.0.0 4.0.0.0 System.Net.Mail.MailPriority The email has high priority. Field 2.0.0.0 4.0.0.0 System.Net.Mail.MailPriority The email has low priority. Field 2.0.0.0 4.0.0.0 System.Net.Mail.MailPriority The email has normal priority.