Each MOC was different for DS. One you request a packet online, one you request a packet via a written letter, one the entire process online. My son was advised (by family of 2016 applicant) to follow their policies but to also snail-mail to all three 1.) asking for an application/confirming that they are starting an application 2.) asking to be included in any invites for academy events.
If you google around online you will find a template on how to write a formal letter to an MOC. Be sure to include appropriate format, title, address, signature line.
For now on (IMHO)every single thing written is:
1. written by the candidate themselves-not ever by the parent
2. formatted formally
3. quadruple checked for spelling and grammatical errors.
3. assumed that every email, mail, fax etc will be looked at by an admission board of some sort or another.