As Neil says, use it if the message is formal. This is the way I was taught is the correct way to do this......
I use this always that I have an attachment. I have never had anyone ask what it means, so I assume that it is clear.......
You will also see many informal things in emails, such as; r u there, pls, u r ..., lol. You can choose you balance of all these things, correct & incorrect, formal & informal as you think appropriate to the email & the audience.