mkimapdcert: 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/mkimapdcert - from package: courier-imap-ssl

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

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