As requested, here is my formal resignation from XYZ Company.
I enjoyed my time working with your firm and am grateful to have had the opportunity to say goodbye to the team. Of course, I knew that my contract would come to an end at this time, but I never anticipated the friendships I built here. I hold you and the rest of the XYZ crew in the highest regard.
I have already signed a contract with ABC Company that will run through next year, but please feel free to reach out to me if you have any needs that I can fill on a per diem basis.