ftpmail: 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
/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/ftpmail - from package: proftpd-utils

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