Dear Mr./Ms. Bossname,
When the time is right, this letter shall serve as my formal resignation from the company. It shall serve as a standing resignation, as we discussed, and will be effective at the time you accept it, in alignment with the company’s needs.
I understand that this is in the best interest of the company as well as myself.
I am eternally grateful for my time with the company, and for all that I have learned here. The growth I have experienced is immeasurable.
Thank you in advance for accepting this open-ended resignation.