Incorrect syntax near '+' in stored procedure sql server
The msdb.dbo.sp_send_dbmail procedure (or other procedures) only accept either a parameter or a literal value.

Consider changing the execution of sp_send_dbmail to this:

SET @usage_data += ' end of data'

exec msdb.dbo.sp_send_dbmail 
@profile_name='some_mail_profile',
@recipients=@admin_list,
@subject='Mail from sql server',
@body=@usage_data,
@importance='HIGH' ;


An example with a user defined stored procedure:

CREATE PROCEDURE dbo.bla(@dbname varchar(255))
as 
SELECT * 
FROM sys.databases  
WHERE NAME = @dbname;
GO

DECLARE @dbname varchar(200);
SET @dbname ='Half';

EXEC dbo.bla @dbname+'OtherHalf';



  Msg 102, Level 15, State 1, Line 46 Incorrect syntax near '+'.