pop3browser: 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/pop3browser - from package: pop3browser

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

Error in other languages:
pop3browser: bevel nie gevind nie
pop3browser: comandă negăsită
pop3browser: comando não encontrado
pop3browser: commande introuvable
pop3browser: command not found
pop3browser: käsku ei ole
pop3browser: không tìm thấy lệnh
pop3browser: komanda nerasta
pop3browser: Kommando nicht gefunden.
pop3browser: kommandot finns inte
pop3browser: komut yok
pop3browser: nie znaleziono polecenia
pop3browser: níor aimsíodh an t-ordú
pop3browser: no se encontró la orden
pop3browser: no s'ha trobat l'ordre
pop3browser: opdracht niet gevonden
pop3browser: parancs nem található
pop3browser: perintah tidak ditemukan
pop3browser: príkaz nenájdený
pop3browser: příkaz nenalezen
pop3browser: команда не найдена
pop3browser: командата не е открита
pop3browser: 命令找不到
pop3browser: コマンドが見つかりません