you cannot append values, or assign variables to the parameters in line:
--not allowed
@subject ='Number of unprocessed records on SQL1 ' + cast(@recordcount as varchar(10));
--the replacement
DECLARE @mysubject varchar(500) = 'Number of unprocessed records on SQL1 ' + cast(@recordcount as varchar(10));
EXEC msdb.dbo.sp_send_dbmail
@profile_name = 'DBA_Mail',
@recipients = 'paresh.motiwala@gmail.com',
@body = 'The count of the unprocessed records.',
--assign the parameter to a variable that did the work
@subject = @mysubject
Lowell