sieveshell: 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/sieveshell - from package: cyrus-imapd-utils

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

On Debian possible default full paths are:

/usr/bin/sieveshell - from package: cyrus-admin

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

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