The email has high priority.
Syntax
MailPriority High
Requirements
Namespace: System.Net.Mail
Assembly: System (in System.dll)
Assembly Versions: 2.0.0.0, 4.0.0.0
Since: .NET 2.0
Assembly: System (in System.dll)
Assembly Versions: 2.0.0.0, 4.0.0.0
Since: .NET 2.0