In this particular case as with most cases, the client prepares the header and the SMTP server sends it. So this would not be the server's time, it would be from the client machine if they are using a client. If that's the case, I would compare the time on the client machine against the header. Please let me know if this doesn't work for you. Of course you are also always welcome to submit a ticket via the link at the bottom of this post as well.
Well that's what I was thinking at first as well, however, I just did another test by sending directly from the webmail on the server out to an external account, and when I grep through my exim_mainlog sure enough the time shows 15:19:03 when it is really 15:48:02.
Now, on this particular account the customer uses postini as an external anti-spam software. Now in his mail-headers when he gets mail I see where postini has timestamped it correctly...but our server seems to have the wrong time.
When I go to the server-time in the WHM it shows the correct time there?
Oh, one more thing I just noticed...all the logs are logging at the incorrect time...I just looked at the /var/log/messages and it is showing the 30 or so minute wrong time as well.
So I guess the bigger question is where do the logs get the timestamp from?