Write a letter informing
about your resigning from your post.
This is to inform you that with great sorrow I am, hereby tendering my resignation to you.
I believe the reasons leading to this decision are well known by you, therefore I shall
leave them unsaid at this time.
I would like to express my appreciation for having had the opportunity of being a member
of (name of firm) for so many years and offer my best wishes for your continued success.