How to set up sendmail on your Ubuntu LAMP localhost

This is beautifully simple:
Step 1. Open up a terminal and type

sudo apt-get install sendmail
This will install the complete sendmail application. It will take a minute or so to complete.

Step 2.  Open up a terminal and type

hostname

This will display your hostname.

Step 3.  Open up a terminal and type

sudo gedit /etc/hosts

or whatever text editor you like using to open up your hosts file for editing.

Step 4. Modify the first line so it reads

127.0.0.1    localhost localhost.localdomain yourhostname

Restart your computer.

It will now work.