Exchange 2007: Duplicate Mailbox Contacts

Exchange 2007 and duplicate contacts, possibly caused by iPhone synchronisation.

Duplicate remover tools may fail due to the sheer quantity - in my case I had approximately 177000 contacts.

1. Temporarily disable ActiveSync on mailbox
2. Export entire Contacts folder in Outlook to temporary PST file - this is your backup
3. Create new PST file, examine date modified / date created fields of the contacts, create new Contacts folder in temporary PST file and copy
4. Run the following PowerShell command on the Exchange server to delete the contents of the Contacts folder:

Export-Mailbox -Identity USER -IncludeFolders '\Contacts' -DeleteContent

- This may take some time - be patient and monitor progress using the following PowerShell command:

Get-MailboxFolderStatistics -Identity USER -FolderScope Contacts

5. Restore the contacts from the temporary PST file