One of our users is getting the message "this e-mail message cannot be delivered to XXX because the e-mail address is no longer valid" . I logged on to her computer, started addressing the e-mail and when the staff name came up I deleted it. Then I used the address book to find the staff name. After I selected it, the same message was display that it was no longer valid. I sent a test email from my Outlook 2010 account to the same user and it worked fine.
What would cause this form a single user.