akonadi_mailfilter_agent: 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/akonadi_mailfilter_agent - from package: kmail

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

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