mimegpg: 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/mimegpg - from package: sqwebmail

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

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