ecff48ad_ion_using_Domain_User_Accounts__2
[0] Excel Services unattended service account [1] The account that Excel Calculation Services uses to connect to external data sources that require a non-Windows user name and password string for authentication. If this account is not configured, Excel Services will not attempt to connect to these types of data sources. Although the account credentials are used to connect to non-Windows data sources, the account must be a member of the domain in order for Excel Calculation Services to use it. [3] Must be a domain user account. [4] Must be a domain user account. [5] Must be a domain user account. [6] Must be a domain user account. [2] 
Must be a domain user account.
MOSS How to ...: Starting and Configuring Office SharePoint Server Search for a web server with Least Privilege Administration using Domain User Accounts
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