Removing E-Mail Alert message

Hi there,
this is my first time ver writing in a forum! hope i will go well.

i have a licent that keep getting the following message:

"Your message did not reach some or all of the intended recipients.
Subject: Exchange Store Size Cameron Broom: 2011-01-12
Sent: 12/01/2011 07:53
The following recipient(s) cannot be reached:

alberto@microsolv.co.uk on 12/01/2011 08:00
The e-mail account does not exist at the organization this message was sent to. Check the e-mail address, or contact the recipient directly to find out the correct address.
"

this e-mail is getting forward message to my server and im trying to find the place that i can remove alberto's e-mail.
alberto e-mail is not valid anymore since he is not in the company and im trying to find out

would be great if someone can help!
thanks in advance,

Offir