tnef.sh: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/tnef.sh - from package: tnef

You may install the required package with command yum install {package}

Error in other languages:
tnef.sh: bevel nie gevind nie
tnef.sh: comandă negăsită
tnef.sh: comando não encontrado
tnef.sh: commande introuvable
tnef.sh: command not found
tnef.sh: käsku ei ole
tnef.sh: không tìm thấy lệnh
tnef.sh: komanda nerasta
tnef.sh: Kommando nicht gefunden.
tnef.sh: kommandot finns inte
tnef.sh: komut yok
tnef.sh: nie znaleziono polecenia
tnef.sh: níor aimsíodh an t-ordú
tnef.sh: no se encontró la orden
tnef.sh: no s'ha trobat l'ordre
tnef.sh: opdracht niet gevonden
tnef.sh: parancs nem található
tnef.sh: perintah tidak ditemukan
tnef.sh: príkaz nenájdený
tnef.sh: příkaz nenalezen
tnef.sh: команда не найдена
tnef.sh: командата не е открита
tnef.sh: 命令找不到
tnef.sh: コマンドが見つかりません