sendmail.mandrill: 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/sendmail.mandrill - from package: python-mandrill

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

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