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.