Did you get a debian VPS server and it already has apache, sendmail and various other junk installed? And the server provider doesn’t have a minimal debian distribution to install? This should pretty much set the server back to a minimal distribution so you can install the web server and mail packages of your choice…
apt-get remove apache* sendmail* bind9* samba samba-common sasl2-bin; apt-get purge apache* sendmail* bind9* samba samba-common sasl2-bin