As a result of the brief and rapid nature of texting and Twitter, emails have become shorter and more informal. In a personal context, it’s OK, but in a professional setting you need to proceed with caution.
Generally speaking, emails should be treated as formal notes unless you are writing to a close professional contact. Emails are misinterpreted all the time, which is why you need to write and edit them carefully. When you write, you lose facial expressions and intonation in speech. Therefore, what you write can be grossly misconstrued and cause undue harm to your professional reputation and relationships.