When you try to send E-mail from your SQL Server 2005 T-SQL with xp_sendmail, there will be an error message shown as follows:
xp_sendmail: Procedure expects parameter @user, which was not supplied.
And probably when you try to pass @user also, it will say invalid parameter.
It seems in SQL Server 2005, xp_sendmail is obsolete and we can use sp_send_dbmail instead.
Following is the syntax:
@subject = 'SQL:DataBase Mail Test',
@body = 'Hello Test From SQL.Hello Test From SQL.',
@profile_name = 'The Profile you created in Configure Database Mail',
@body_format = 'HTML'
The following link has screen shots to setup Email Profile in SQL Server : Click Here
Hope it helps