How to: Create a Proxy (SQL Server Management Studio)
Microsoft SQL Server Agent proxy accounts define a security context in which a job step can run. To set permissions for a particular job step, create a proxy that has the required permissions for a SQL Server Agent subsystem, and then assign that proxy to the job step. Only members of the sysadmin fixed server role have permission to create, modify, or delete proxy accounts. Users who are not members of the sysadmin fixed server role must be added to one of the following SQL Server Agent fixed database roles in the msdb database to use proxies: SQLAgentUserRole, SQLAgentReaderRole, or SQLAgentOperatorRole. For more information, see How to: Configure a User to Create and Manage SQL Server Agent Jobs (SQL Server Management Studio).
After upgrading from SQL Server 2000 to SQL Server 2005, all user proxy accounts that existed before upgrading are changed to the temporary global proxy account UpgradedProxyAccount. The UpgradedProxyAccount is only granted access to those subsystems that were explicitly used, and does not have access to all subsystems after upgrading.
To create a proxy account
In Object Explorer, expand a server.
Expand SQL Server Agent.
Right-click Proxies and select New Proxy.
On the General page of the New Proxy Account dialog, specify the proxy name, credential name, and description for the new proxy. Note that you must create a credential first before you create a proxy if one is not already available. For more information about creating a credential, see How to: Create a Credential (SQL Server Management Studio) or CREATE CREDENTIAL (Transact-SQL).
Check the appropriate subsystem for this proxy.
On the Principals page, add or remove logins or roles to grant or remove access to the proxy account.