We are using Office365 for our email service with Outlook 2010.
I have one user who relies on autocomplete when composing email, like many of us do.
However, he noticed a situation where he will use AutoComplete, it will find an address that we all know exists, populate the to field with it, and then say this address do not exist.
However, when he does the same thing using the address book and fills it in that way, it does exist.
Not sure what this could be.