XCON: High Priority Mail Sent from MS Mail to Internet Changes Priority

Internet mail messages sent as high priority (urgent) from a Microsoft Mail postoffice (with an SMTP access component), over the MS Mail Interchange to a Microsoft Exchange Server computer, and then over the Internet Mail Service, may change priority. The priority may also change if the message travels across an X.400 connector to the Internet Mail Service.

You can see the change in priority by looking at the Internet Mail Service queue after the mail is delivered to the Microsoft Exchange Server computer. If the destination host is not available, the message is queued and the expiration time is set to 48 hours, which is the default for normal priority messages. View the message in the Imcdata\Out directory, and it will have X-Priority set to 1 (normal). The MS Mail sender may not receive notification messages that the message is queued for delivery, but not yet delivered.

The Internet Mail Service uses the PR_PRIORITY property from the envelope (P1) instead of the PR_IMPORTANCE property. The Internet Mail Service bases the calculation of expiry times on the value in PR_IMPORTANCE of the message.

Microsoft has confirmed this to be a problem in Microsoft Exchange Server version 5.0. This problem has been corrected in the latest U.S. Service Pack for Microsoft Exchange Server version 5.0. For information on obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

The message flow is as given below:

The MSMI creates an X.400 P1 and a message in the form of MDB Extended Format (MDBEF), and then submits it to the MTA via X.400 API (XAPI). In this P1 there is no PR_IMPORTANCE since it is a P2 property. PR_PRIORITY is set in the P1 and also in the MDBEF. The information store picks this up from the delivery queue and creates a hybrid P1, which has all the X.400 P1 properties, plus some P2 properties. Some of the selected P2 properties are promoted into this new P1 envelope, but PR_IMPORTANCE is not one of them. Therefore, this envelope contains the PR_IMPORTANCE, but with a default value of Normal. This new envelope is put in the MTS-OUT queue for the Internet Mail Service. The Internet Mail Service picks up this envelope from the MTS-OUT and reads the properties from the envelope. The Internet Mail Service is reading the PR_IMPORTANCE to decide the priority of the message. Because the information store created this envelope and never promoted the real PR_IMPORTANCE, a message with priority Normal occurs. The PR_PRIORITY in this envelope is set to Urgent, because it was correctly passed through from the MSMI and the information store.

For this issue, the Internet Mail Service has been changed to use the PR_PRIORITY from the P1 instead of PR_IMPORTANCE. PR_IMPORTANCE indicates a value to users, while PR_PRIORITY indicates the order or speed at which the messages are sent by the messaging system software. Higher priority usually indicates a higher cost. Higher importance usually is associated with a different display by the user interface.