"Since PAB (personal address book) entries are not updated when e-mail addresses are changed or removed on the Exchange server, it is recommended that you use Outlook Contacts rather than a PAB. Outlook Contacts are stored as part of your mailbox, rather than a separate file, which makes them available to you even when you are opening your mail remotely.
If you have a PAB with entries in it, you can convert these into Outlook Contacts. If you have been using Contacts as well as the PAB you may have duplicate entries in these folders. When you import the PAB into your Contacts the duplicates are not automatically removed. Before doing the import, take a look at the entries in both of these folders. If an entry exists in both folders verify that the entry in Contacts is accurate, and then delete the duplicate entry from your PAB...."
See
http://usfweb.usf.edu/usfit/exchange/Outlook_2000_hints.htm#_Personal_Address_Book/Contacts
for the rest of this.
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