dmail: 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/dmail - from package: uw-imap-utils

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

On Debian possible default full paths are:

/usr/bin/dmail - from package: uw-mailutils

You may install the required package with command apt-get install {package}

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