Unfortunately few most important mails has been deleted from inbox, not even available in trash folder. How can I recover those mails. Please. Help me.

Highly unlikely that you will be successfully.

Its not easy but there is a chance.

The quicker you do this the better.

Find out what format your email programs uses for it's email databases.
*.dbx (Outlook Express)
*.pst (Mirosoft Outlook)
...
...
...

Download and run Recuva here Recuva Review (v1.49.1019)

Do a full nor a quick search.

Rifine your search with the extension of you email program example:
Microsoft Outlook files serch (type the following in the Recuva Program: *.pst )

If will take a long time to search.
Once done copy all the version of the pst files to an external hard drive NOT back onto the PC.

Open the mail program an add the database file to your emails.
Chance are bad but there is a chance.

Ask someone who knows computers to help you a little with the steps.

There are also programs online that can recover mail from databases but you need to find the deleted versions with Recuva first.

Hope this helps
Grant