Depending on your storage destination, you must configure the following:
Avaya message store: You do not need to perform any configuration.
Exchange 2007 or Exchange 2010: For Exchange, the service account is a normal Active Directory Domain User account with an Exchange mailbox. You must provide Exchange Impersonation permissions to the account. Exchange Impersonation enables a caller to impersonate a given account so that a caller can perform operations by using the permissions that are associated with the impersonated account instead of the permissions that are associated with the account of the caller.