Dear …
It is with mixed feelings that I announce to you today, the decision I have made to leave my position of __(name of position)__ with __(name of organization)__. I have been presented with a new opportunity that I am anxious to pursue. This wasn`t an easy decision for me, but after long consideration I have decided that the timing is right for me to move ahead with this career change. My last day here will be __(date)__.
It has been my pleasure to have worked with such wonderful people as you. You all have made my time here most enjoyable. I will miss the many relationships and friendships I have built here over the last __ (#) __ years which makes it very hard for me to say goodbye.
I just wanted to express my thanks to all of you who have been there for me with support and help whenever I needed it. I feel very fortunate to have been part of a team of such fine individuals. With my greatest sincerity, I wish each and every one of you all the very best life has to offer for many years to come!
Sincerely,