userdb-test-cram-md5: 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/sbin/userdb-test-cram-md5 - from package: courier-authlib-userdb

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

Error in other languages:
userdb-test-cram-md5: bevel nie gevind nie
userdb-test-cram-md5: comandă negăsită
userdb-test-cram-md5: comando não encontrado
userdb-test-cram-md5: commande introuvable
userdb-test-cram-md5: command not found
userdb-test-cram-md5: käsku ei ole
userdb-test-cram-md5: không tìm thấy lệnh
userdb-test-cram-md5: komanda nerasta
userdb-test-cram-md5: Kommando nicht gefunden.
userdb-test-cram-md5: kommandot finns inte
userdb-test-cram-md5: komut yok
userdb-test-cram-md5: nie znaleziono polecenia
userdb-test-cram-md5: níor aimsíodh an t-ordú
userdb-test-cram-md5: no se encontró la orden
userdb-test-cram-md5: no s'ha trobat l'ordre
userdb-test-cram-md5: opdracht niet gevonden
userdb-test-cram-md5: parancs nem található
userdb-test-cram-md5: perintah tidak ditemukan
userdb-test-cram-md5: príkaz nenájdený
userdb-test-cram-md5: příkaz nenalezen
userdb-test-cram-md5: команда не найдена
userdb-test-cram-md5: командата не е открита
userdb-test-cram-md5: 命令找不到
userdb-test-cram-md5: コマンドが見つかりません