I am writing to notify you that I will be resigning from [company], effective [date]. I will be assuming a new role at [new company].
I have thoroughly enjoyed my time here and took great pleasure in working with you. I am thankful for all of your support, advice, and instructions during my stay at this company. I know that I will be missing everybody here, but I am also thrilled about taking this next step in my career path. I am thankful for the insights you shared, as they will be helpful for the next challenges I will encounter.
I hope that you do keep in touch. You can call me at [phone number]. Thank you so much for everything.