Read http://answers.microsoft.com/en-us/windows/forum/windows_7-networking/contacts-list-disappeared-from-windows-live-mail/7ff07a34-9203-4f73-9f88-95d6ddaa75e7 and ask in their support forum.
When I write an email and click on the "To" box to insert an address, I only see some of my addresses...not the entire list. I have about 200 contacts in my Contacts folder but they don't all show up when I create an email. I have to create a new contact if I want it to show up in the email address box even though that contact is already listed in my Contacts folder. How can I correct this so ALL of my contacts in my Contacts folder are available when I write an email?
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