Last time we had a time change, my email client PowerMail 4.x reflected the change correctly. I have discovered that PowerMail 5.0.1 has a bit of a bug in it. I believe it checks in with the Date & Time preference pane (OS 10.2.6) upon starting up, but never again until the next startup [which actually doesn't sound so bad]. All I needed to do to solve my time problem was restart PowerMail.
Yeah, rocket science. If your clock doesn't adjust to the time change (which happened today in most of the USA), restarting PowerMail solves the problem. If, like me, you rarely restart anything, this apparent bug in PowerMail would not otherwise easily resolve. ---Jay