notification.php

<?php
// Route to user address from drop down list, update the '1' to the ID of your form – I am using this on 6 forms so I have removed the ID requirement
add_filter( 'gform_notification', 'welcome_email', 10, 3 );
function welcome_email( $notification, $form , $entry ) {
	foreach( $form['fields'] as &$field ) {
		// Similar to above, find the right field
		if( $field['type'] != 'select' || strpos($field['cssClass'], 'user-emails') === false )
			continue;
		
		// Pull out the user id selected, by the field id and the $entry element
		
		$field_id = (string) $field['id'];
		$user_id = $entry[ $field_id ];
	}
	
	// create a variable based upon the user ID
	if( !empty( $user_id ) ) {
		$welcome = 'Dear ' . get_the_author_meta( 'display_name', $user_id ) . ',';
	}
	
	// this appends the variable to the foot of the notification
	$notification['message'] = $welcome . $notification['message'];
	
	return $notification;
}