How to send email directly without opening the outlook when clicking submit button in HTML?

HTML can't do that - it runs on the client, so it has to access client resources in order to send an email. That means that an HTML email request has to use the client email app to generate the email - and if you think about it, that makes a lot of sense, unless you want random websites sending out emails in your name without your knowledge!

The only way to send an email without opening the client email app is to send it from the server, using server email ids and server code. Exactly how you do that will depend on the language you wrote your server side code in: C#, VB, or PHP for example.
A quick google will find you examples of sending emails from the server, if you include your chosen language.

Quote:

I need to send email when submit button is Clicked.

There is basically 2 solutions:
- On client side: By using a link like <a href="mailto:someone@example.com?Subject=Hello">Send Mail</a>
The link opens a new mail on client side, but sending the mail or not is a client choice, its contain too.
- On server side: Just like in solution 1, you must call some code on server which will do the job.