Dear Mr. Alvin,
I wish to inform you that I shall be resigning from my job on 07 March 2xxx. I will be taking up a new appointment in Thailand.
My stay here has been a beneficial one and I learned a lot under your guidance. I thank you very much for everything you have done for me.
However a better opportunity awaits me and I have to take it. Furthermore Thailand is nearer to my home town, Malaysia, so I can be closer to my family there. Thank you.
Yours sincerely,