Eu colocaria os destinatários na mensagem e usaria o sinal -t
do sendmail:
#Email Settings
Message_Success="Database Backup generated successfully"
Message_Failure="Problem occured while generating Database Backup please verify"
Subject="Database Backup Status Mail"
Sender_Name=DatabaseBackup
Recipients="[email protected],[email protected]"
sendmail -F $Sender_Name -it <<END_MESSAGE
To: $Recipients
Subject: $Subject
$Message_Success
END_MESSAGE