The title says it all. I have customized the Maintenance mode page, to Coming soon!! how i want to enable the visitors of the website to Subscribe So they'll will be notified when the website is officially lunched. how can i Achieve this, am developing the website in Drupal in 7.
Don't put your sie in permanent "maintenance mode". Instead use the Rules module to achieve the same goal.
All that's needed is some tuning of the "Custom rule" I suggested also as an answer to the question about "How can I put a Drupal Commerce site in 'Shop Closed' mode, similar to Drupal's maintenance mode?".
In your case you'd probably want to block mostly every URL being visited, except the "User registration" page.
I have prepared a step by step guide for allowing the anonymous user to subscribe for the node update.
Visit this link for a complete guide: http://c.pachabhaiya.com/blog/2013/08/drupal-how-to-make-anonymous-user-subscription-on-a-particular-node-update/
Possibility for the anonymous users to subscribe to particular node.
Send email notifications automatically to the subscribed users when
that particular node is updated.