Write a letter of resignation from post.

This is to inform you that I have been presented with an opportunity that will enable me to work in the area of my stated preference, which is marketing. Therefore, I am tendering my resignation from (name of company) and wish to inform you that (Date) will be my last day of employment.

I would like to thank you for the experience of having worked for your company, which is a truly outstanding organization. I wish you best wishes for your continued success.

Sincerely,