Many students fail to take advantage of free resources. There is nothing wrong with sending an introductory email or letter to a school. The most important thing is the content of the email. If you send an email asking questions that are already listed on their website, you will most likely come across as a candidate that is not thorough. However, if you ask salient questions, this just might make an impression. Be informed though, that sending an email or not, does not necessarily impact your application positively. The admissions committee looks at your application documents independently. Also, do not harass administrative staff or faculty with emails, as this is likely to give you a bad reputation. Finally, if you decide to send emails, ensure that there are no typographical errors and address your email appropriately!