I wouldn't use 'excited' to describe an email shares news that makes both of you happy. "Excited" only talks about the manner in which the person wrote it.
There are several things you mights say, You might call it a 'happy email' because the other person was happy when he wrote it, and reading it made you happy.
However, I wonder whether you are thinking of 'exciting'. An exciting email would be one that made you excited, as I think you were when you received the email. It shows that you share the feeling with your friend.
Actually I wanted to express the manner in which the email was written --- the mailer is excited.
However, as you suggest, 'exciting' is better than 'excited' in such a case because I was excited by the email --- both of us are excited.
Thanks for all the suggestions.
Now I know how I should reply to my friend.