That's a very difficult task, as being a friend, you would typically use local phrases, idiom and greetings that you both would know! If it was an email to a friend, I often wouldn't use any introduction or ending at all! If I did, I would probably just use 'Hi', or 'Hi Antonio' to start, and 'cheers' or 'seeya' to finish. Again though, 'cheers' is more common here in the southern hemisphere. You could write a draft in a notebook entry, and see what people suggest.

The notebook entry is a good idea. I would suggest this an an approach: email, being informal, is more like spoken English. So, imagine what you would say to your friend if you were speaking to him, and then write it down. From the assignment, can you tell whether you are going to be graded on spelling, punctuation, and grammar?