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If you're a Gmail user and you visit this page, you'll get an error message and Gmail will redirect to a page that shows the oldest messages from your account. This is the oldest message from my account:
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Gmail was launched on April Fool's Day of 2004 and that first email I sent from Gmail is dated June 12, 2004. That means I didn't get my invitation for over two months.
I'm willing to bet one of you was using Gmail before me. Does anyone have an earlier start date with Gmail?