Event ID - 15000

Event Id15000
DescriptionThe mailbox for user <user name> already exists, and may have been created during a previous migration. Check for duplicate mail.
Event InformationAccording to Microsoft:
This problem can occur because command-line mode migration matches X500 address only, unlike wizard-mode migration, which matches security identifier (SID), X500 address, or both.
To work around this problem, add a source X500 e-mail address to the new account in Active Directory. If you do so, command-line migration then finds the existing account and migrates mail to the new mailbox. You can either use script to add an X500 address to users, or add an X500 address manually. To manually add an X500 address:
1. In the Active Directory Users and Computers Microsoft Management Console (MMC) snap-in, open the properties of a user that you want to add an X500 address to.
2. Click the E-mail Addresses tab.
3. Click New, and then click Custom Address.
4. In the E-mail address box, paste the "Obj-Dist-Name" from the mailbox object in the Microsoft Exchange Server 5.5 Exchange Server Administrator program (Raw mode).
5. In the E-mail type box, type X500.
6. Click OK twice.
Reference LinksXGEN: Exchange 2000 SP1 MAPI Migration Does Not Match SID When Run from a Command Line

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