This mostly due to you overwrite some config files during upgrade.
Ideally, you should not overwrite config files, unless something very important exists inside new config files.
To fix situation, try these:
login to ehcp, options-> fix mail configuration.
this fixes many configuration files.(mail, ftp etc.)
check your /etc/apache2/apache2.conf file,
and add following lines if not exists:
after that, restart apache:
if still problem, let me know whats not working.