XFOR: SMTP Header Time Conflicts with Sent Time on Message (156965)

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When the originator transmits a message, Microsoft Exchange will attach the date, time, and Greenwich Mean Time (GMT) offset. These values reflect the time that the message left the originator's Outbox. However, when a Microsoft Exchange client displays the message in the recipient's mailbox, it converts the time that the message was sent to the equivalent time in the recipient's time zone. For example, if I am located in Seattle and send a message to you at 1:00 PM (13:00) Pacific Daylight Time and you receive the message in Charlotte within 15 seconds, the time showing in the Sent field of the message will be 4:00:15 PM (16:00:15). Depending on the time settings of the respective Microsoft Exchange clients and Microsoft Exchange Servers involved, the SMTP Header information on the originating message will show: 13:00:00 (-07:00) or 13:00:00 (PDT) and the time stamp from the receiving server will show 16:00:15 (-04:00) or 16:00:15 (EDT). Note that the GMT offset may be expressed as either a numeric value, - 04:00, or an alphabetic label, EDT.

Microsoft Exchange accomplishes this conversion in a two step process. First, it converts the time that the message was sent to GMT. Second, it converts the GMT time of the message to the local time of the recipient. In the example above, it would first convert the 13:00 PST sent time to 20:00 GMT and then the 20:00 GMT to 16:000 EDT. The 15 second actual transmission time is also added to the Sent: time to produce the final time displayed on the message.

Time zone offsets West of Greenwich are expressed as negative numbers and time zone offsets East of Greenwich are expressed as positive numbers. The Microsoft Exchange client does not recognize all alphabetic time zone labels. In fact, it can only convert ten alphabetic time zone labels to their numeric equivalents. The recognized time zones are:

   Time Zone Label      Numeric Offset
   ===============      ==============
        GMT                +  0:00
        UT                 +  0:00
        EST                - 05:00
        EDT                - 04:00
        CST                - 06:00
        CDT                - 05:00
        MST                - 07:00
        MDT                - 06:00
        PST                - 08:00
        PDT                - 07:00
				

All other alphabetic time zone labels are ignored. For those time zones, the result will be that the message time will be off by the exact amount of the GMT offset for that time zone.

Why does Microsoft Exchange handle time zone values this way? Because that's the way RFC 822 defines time zones. According to the RFC, the only time zones with recognized, or official, time zone labels are the ones listed above. So Microsoft Exchange is functioning in a way that is literally compliant with the applicable RFC. To do otherwise would take us out of compliance.