When you are resigning from your current position, you have to send formal resignation email to your manager. It also serves as evidence to HR department and your notice period will be count from the date of resignation.
Subject: Formal Resignation
Hi Mr. X,
I would like to inform you that I am quoting my resignation from my current position as Application Development Senior Analyst with effect from 11.06.2017, due to my family emergency.
I request you to please accept my formal resignationand relieve me as soon as possible.