Maurice's Outlook contacts disappeared and now he can't send group emails. Leo says there could be a few things happening. Outlook's autocomplete is constantly looking at the contacts, and if it's missing, then it can't read them. If it's intact, then it should come out, including his group list. Carbonite will backup his data, but if the link between his contacts and the group list is broken, then that could be part of the problem. He should try and verify that his address book is there. If the address book is gone, then there is the problem. If the list is there, then he can back it up.
Leo also says that the autocomplete for lists may have been disabled. He can check this out by going to File > Options > Mail, and under "send messages" he should see if "use autocomplete to suggest names when typing" is checked. If it's not, then he should check it. It may have been disabled somehow. Here's a tech note from support.microsoft.com that may help.
This problem can become a tricky one quickly, and that is why Leo generally recommends an iPad or Chromebook instead of Windows.