Exchange Server 2010 Alias Issue

Dear Fellows,

One of my client is facing an issue with Exchange 2010 since the day we migrated them from Exchange 2007 to Exchange 2010. Right now both exchange are in coexistence. (Exchange 2007 SP2 and Exchange 2010 SP2 RU4)

Customer has a practice to create account with Pre-Windows2000 Logon name as Employee ID (Lets say 12345) and the normal logon name as FirstName.LastName (Lets say John.Smith).

Now when they mail-enable this user account on Exchange 2007, they get John.Smith as email alias. But when they mail-enable a user on Exchange 2010, it generates a mail alias as 12345.

Required settings are to have John.Smith as the Alias on Exchange 2010. Does anyone have any idea on it?

Thanks.

Junaid Ahmed