X400: How MS-DOS and Windows Priorities Convert to X.400

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The most commonly used priority setting fields in X.400 are the P1 UMPDU Envelope Priority and the P2 IM-UAPDU Heading Importance field. These fields are generated by MS-DOS client priorities 1 and 5, and by Windows client priorities low and high. Priorities 2 through 4 (for the MS-DOS client), or normal (for the Windows client) do not generate the Priority or Importance fields.

The Priority field (part of the P1 UMPDU Envelope) affects the delivery time of the message within the X.400 system. MTAs favor high priority to lower ones when forwarding messages to the next MTA.

The Priority field can have these values: The Importance field is a part of the P2 IM-UAPDU Heading. This field does not affect the delivery time--it simply indicates a level of message importance in the recipient's user agent(UA).

The Importance field can have these values: The following tables illustrate how Microsoft Mail client priority settings (MS-DOS and Windows) are converted into X.400 settings:

MS-DOS client   P1 Priority field     P2 Importance field
-------------   -----------------     -------------------
 
   1            1 (non urgent)          0 (low)
   2            - (not generated)      - (not generated)
   3            - (not generated)      - (not generated)
   4            - (not generated)      - (not generated)
   5            2 (urgent)             2 (high)
 
 
WIN client   P1 Priority field     P2 Importance field
----------   -----------------     -------------------
low          1 (non urgent)          0 (low)
normal       - (not generated)       - (not generated)
high         2 (urgent)              2 (high)