My first thought was that they had obtained an account on orbisonline.com (it's mail is hosted by eoutlook.com ), so they could have had a "stolen" account.. and that they were testing for valid email addresses...
However, communication with eoutlook.com tells me that the account doesn't exist.
$ telnet exchange.eoutlook.com 25
Trying 66.225.227.39...
Connected to exchange.eoutlook.com.
Escape character is '^]'.
220 exchange.eoutlook.com Microsoft ESMTP MAIL Service, Version: 6.0.3790.211 ready at Tue, 21 Nov 2006 01:31:05 -0600
HELO
250 exchange.eoutlook.com Hello [XXX.XXX.XXX.XXX]
MAIL FROM: [email protected]
250 2.1.0 [email protected]er OK
RCPT TO: [email protected]
550 5.1.1 User unknown
RCPT TO: [email protected]
250 2.1.5 [email protected]
It may have existed initially and that's what it was used for... and has been found and eliminated... It's hard to say for sure... Especially since I can't find any records of anything similar online.