On Thu, Aug 27, 2015 at 11:32:13PM -0700, aparsloe wrote:
> [The system date on my computer is correct. I can't see a setting for time
> in Thunderbird. But I do live reasonably close to the International Date
> Line.]

  The problem is with the time zone.  The date and time are correct in
your time zone, but are incorrectly marked as UTC-7, i. e. US Pacific
Time, instead of New Zealand time (UTC+12).  Your emails thus
systematically appear to have been sent 19 hours in the future.