clamd.clamsmtp: command not found

Have You tried accessing the binary with the full path?

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/clamd.clamsmtp - from package: clamsmtp

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