Most people don't realize that their PC is the source of the timestamp affixed to every message, (unless you're using your provider's webmail). Even if the PC's clock appears current, email will arrive in the recipient's mailbox out-of-sequence:
11:52 John / here's my replyIn case you're not following the example .. Mary didn't apply the DST patches. In real time, Mary sent an email at 11:45am -- but was timestamped as 12:45pm. John replied seven minutes later (11:52), Mary replied six minutes after that (11:58) and John finished the thread six minutes later (12:04pm).
12:04 John / John's conclusion
12:45 Mary / here's the original email
12:58 Mary / Mary's reply
That could be hard to follow if you're trying to make sense of this email thread. The problem will continue until either:
1- 16 more days pass until DST would otherwise start - on April 1st;
2- the person applies the new DST patches.
Even then, it's not foolproof since the clocks on most PCs wander. On one of my XP boxes, I was forced to install Automachron because the PC wandered up to 8 minutes a day, and there's no obvious way to adjust XP's Internet-sync feature to probe more than once a week.
Related: I watched one TV news show - sometime around March 9th - explain how to "fix" the PC without installing the DST patches: they said to simply (x)uncheck the box related to Daylight Saving Time, then manually (x)check it back on April 1. They must've been Texans because the advice was WRONG, WRONG, WRONG.