popauth: 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 Debian possible default full paths are:

/usr/bin/popauth - from package: mailutils-pop3d

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

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