Outlook doesn’t keep its own time. Outlook uses the system time.
The real issue here is understanding where the “time” comes from when you receive an email.
When you send an email, Outlook applies the current system time to that email and sends it off to wherever it’s going to go. When somebody sends you an email, that message gets marked with the time of the sender. In other words, the system clock on that person’s machine is what’s used to actually mark when the email was sent.
Now, that means a couple of interesting things.
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Sending email to different time zones
If the person sending you email is in a different time zone, the email system has to understand how to account for the time zone difference. As you’ve pointed out, that’s one of the common situations that people run into when they find out that their email times seem to be an hour or more off. One of the machines (either the sending or receiving computer) doesn’t have the correct time zone set. This is more common when Daylight Savings Time comes into play because that changes the time and happens at different times in different countries.
The email infrastructure is actually built to handle all of this.
When email gets sent, the actual time that appears in the email headers (the headers that you normally don’t see) includes universal time (in other words: Greenwich Mean Time, GMT or UTC depending on how you want to look at it) and an indication of how far from GMT the sending location is. So, the email system will actually say something one o’clock and then minus 600 to indicate that it’s six hours from GMT.
Now, that accounts for all of the hour issues and some of the occasional half hour kind of issues.
Five minute differences
In your situations, I believe the person who sent you the email is the one who is off. Or, rather, it’s their computer’s clock that’s off. That’s the one that marks the time when they send email.
I’ve actually experienced this; it’s really, really weird to get an email before it was sent if you were paying attention to the time. The reality is that the sender’s clock and yours differed by five or so minutes (whatever the discrepancy turns out to be).
Unfortunately, there really isn’t a good way for the mail system to account for any of this. It simply has to trust that the sending email program on the sending email machine has the same concept of “what time it is” as compared to wherever the email is being sent.
The bottom line is the difference in time has nothing to do with Outlook and your machine; it’s actually a difference between your machine and the machine of the person that sent you the email in the first place.