zope-sendmail: 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

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/zope-sendmail - from package: python-zope.sendmail
/usr/lib/zope2.13/bin/zope-sendmail - from package: zope2.13

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