There are only five possibilities for name that are legal: special-delivery
This mail message needs to be processed before any others. This precedence is effective only when the message is being delivered from the queue. first-class
Unless otherwise declared with a Precedence: header, the message is first-class by default. list
The message originated as part of a mailing list. It should be deferred until other more important mail has been processed from the queue. bulk
The message is a broadcast, like a mailing list but less important. If the message can't be delivered, the message body is discarded from the bounced mail. junk
Absolutely worthless mail. Test messages and mail from some programs fall into this category. Like bulk, the message body is discarded from the bounced mail.