openpgpkey-milter: 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/openpgpkey-milter - from package: openpgpkey-milter

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

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