Final answer:
The solution of adding the DatabaseMailUserRole to U1 in the msdb database meets the goal of configuring a SQL Server instance for U1 to send mail using Database Mail.
Step-by-step explanation:
The solution provided to add the DatabaseMailUserRole to U1 in the msdb database is true and it meets the goal of configuring a SQL Server instance for U1 to send mail using Database Mail.
By adding the DatabaseMailUserRole to U1, it grants the necessary privileges for U1 to access and use Database Mail. This role allows U1 to send emails directly from the database.
Other roles, such as DatabaseMailUser or DatabaseMailAdmin, provide different levels of access and control over Database Mail, but in this case, the DatabaseMailUserRole is sufficient to achieve the goal of enabling U1 to send mail using Database Mail.