Dear …
Please accept this letter as my formal notice of resignation from __(name of firm)__. __(date)__ will be my last day of employment.
I`d like to express my thanks to you and my colleagues for the opportunities I have been provided with over the past __(#)__ years. The associations I`ve made during my employment here will truly be memorable for years to come.
This wasn`t an easy decision for me, but after long consideration, I have finally made a decision to accept a new position as a strategic career move. Please call on me if I can be of assistance to help train my replacement to ensure a smooth transition.
It has been a pleasure working here and I extend to __(name of company) __, my sincere thanks and best wishes for the future.
Yours truly,