Email shows sent to recipient but actually recieved

. After saving leave application Employee, the messege will show sent to recipient about the leave application but the person is not receiving the email in his inbox.

Have you checked your email queue ? What does it say there?

yes. the status is showing not sent. I clicked on send now button but didnt work

What about your email account ? Properly set ?

yes this the email account

Do you receive emails from that address? if not then I think there is an error while sending emails, perhaps you can check the error log list to see if there is any error traceback to be found there.
If you have been receiving emails from that account then the issue rests solely with the the leave application doctype.
Sharing the error log will be the best way to pinpoint the source of the issue.