amavisd-snmp-subagent: 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 CentOS possible default full paths are:

/usr/sbin/amavisd-snmp-subagent - from package: amavisd-new-snmp

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/sbin/amavisd-snmp-subagent - from package: amavisd-new

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

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