Question:
I am getting the following message: Notice: Undefined index: action in /home/fhlinux170/c/cybernet-designs.co.uk/user/htdocs/formtest.php on line 17.

Line 17 contains this line of code if($_POST['action'] == "send"){

Answer:
This error appears because of your PHP error reporting settings. Usually, it appears when your variable is not properly set. There are two ways to handle this issue:

1. Check if $_POST['action'] is set before using it. For example:

if (!isset($_POST['action']))
{
//If not isset -> set with dumy value
$_POST['action'] = "undefine";
}

2. Suppress Notice warnings

Notice warnings could be suppressed by changing the error_reporting variable in your PHP.ini. error_reporting could be set to show all errors except those for notices and coding standards warnings: error_reporting = E_ALL & ~E_NOTICE

The same is accomplished by adding the following line in your php page:

<?php error_reporting (E_ALL ^ E_NOTICE); ?>