why I am getting e-mail from 1969?

This came up on Facebook, and I thought it worth a quick post here. From time to time you may see e-mail or files with a date of December 31, 1969. What the heck?

The explanation is that many computer systems measure time as the number of seconds since January 1, 1970 12:00 am UTC. (Sort of. Leap seconds make it complicated. See the wik's article on "Unix Time" for the gory details.)

So a time of "0" indicates that date and time -- which in any U.S. timezone, would have been the night of December 31, 1969. (UTC, for most practical purposes, is "Greenwich Mean Time", and so is a few hours ahead of the U.S.)

And if your file doesn't have valid time information attached to it, or your e-mail has a garbled Date: header, the system will treat it as 0, and claim that it's from the dawn of the 70s.

So now you know. And knowing's half the battle.