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Complete the wizard to assign the services to the new SSL certificate.
You will be prompted to overwrite the existing self-signed certificate, so choose Yes to that prompt.
You will notice that the wizard makes a recommendation as to the type of certificate that is required for your Exchange organization.
In most cases a “Unified Communications certificate” will be necessary, which is basically another name for a SAN certificate.
Right-click the new certificate and choose “Assign Services to Certificate”.
Configure legacy names for each of the namespaces in the organization, in this example “legacy.contoso.local” and “legacy.xyzimports.local”.Although you can issue the certificate from a private Certificate Authority it is recommended to use a commercial Certificate Authority such as Digicert.After you have acquired the new certificate return to the Exchange Management Console, navigate to Server Configuration, right-click the server and choose Complete Pending Request.Although wildcard certificates are supported in Exchange Server 2010 it is recommended to use a SAN (Subject Alternative Name) cert instead.
Next we can configure the names for each of the Exchange 2010 services that are secured with the SSL certificate. Enter the internal and external names of Outlook Web App.Browse to the location of the file you downloaded from the CA and complete the wizard.