Date
Dear XX:
Congratulations! I am so glad to hear that you are appointed as an asistant manager in an import and export company. You are efficient and hard working, and I believe that you could do a very good job in the company. I wish that everything goes well with you and I expect to hear about your promotion soon.
XXX
对于这个你可以在网上找一下模板去道客巴巴或者豆丁文库上面,应该能够找到这种核心的这些写法。