dbmail-deliver: 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/sbin/dbmail-deliver - from package: dbmail

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

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