Once you know the proper format of the message then you can start thinking about the content of the message. You should remember that a common mistake in wishing someone happy birthday is sending the message to your friend without giving him any name. This is very unprofessional and can make the person irritated. So what you should do is introduce yourself with the happy birthday message before finishing with your friend's name. This way he will get the desired satisfaction when he open the message.
The next question is how to wish happy birthday to cousin? One of the most important things to do is to consider your relationship with your friend. If you have a good relationship then you can easily open up a door for his being happy on his birthday. But this can be difficult to do if you are living in a different country and do not talk to him regularly. Visit happy-birthday-quotes.com for the best quotes to wish your cousin.
Hence you should try to call him on his birthday and wish him a happy birthday. This can be done by either phone or email. When talking on the phone, you should use the voice tone that your friend often uses. If possible you should also give him your personal information on the phone as you will not feel comfortable telling him that you want to wish him happy birthday in public. However if you cannot call him regularly then you should send him a small gift that can help him in some way to carry his weight on his birthday.