exim_checkaccess: 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/exim_checkaccess - from package: exim

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

On Debian possible default full paths are:

/usr/sbin/exim_checkaccess - from package: exim4-base

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

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