I am trying to figure out what causes my contacts to stop 'auto-filling' in Outlook sometimes.

You know, when you attempt to create a new email and just type in a few characters, then you get a list of possible matches from your contacts are previous email addresses you have sent to.

Sometimes that feature does not work. I am not sure what the feature is called, so I can't trouble shoot the KB for any references.

Anyone had similar troubles?