smtpping: command not found

Have You tried accessing the binary with the full path?

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

[root@server ~]# echo $PATH

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/smtpping - from package: smtpping

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