Impossible to say for sure without knowing a lot more detail.
Here's what I'd guess has happened.
Their ISP gives out an email address in the form of
[email protected]
The ISP will accept emails for
[email protected]
You then have a choice about how the email software can be setup, it can either be setup as
[email protected] or just hostname.provider.com
if it's setup the first way they'll only receive emails addressed to the exact name@
If it's setup the second way they'll receive emails addressed to anything@
I'd guess the first computer was setup to only get emails addressed to the exact name@ and the second one has been setup to get emails addressed to anything@ and the email from 2010 had an error in the first part of the address so it didn't exactly match the name@ on the first computer, so it just would have sat waiting on the server for a computer setup to get emails addressed to anything@.
Also, why do people keep putting questions like this in chatterbank, there is a tech section that is a better place to put tech questions.