Sendmail

If sendmail isn't installed, install it:
```
sudo apt-get install sendmail
```
Configure /etc/hosts file, make sure the line looks like this:
```
127.0.0.1    localhost    yourhostname
```
Run Sendmail's config and answer Y to everything:
```
sudo sendmailconfig
```
Restart apache:
```
sudo service apache2 restart
```