Here it is, the "I Made It!" postcard that you'll be sending home to a chosen loved one when you first arrive at BMT. You'll get only one of these cards, so figure out who's going to get it (ideally before you go) and instruct that individual to pass that address along to every one who may want to write to you. I sent mine to my husband with the explicit instruction that he post my address on our Facebook pages for friends and family. Make sure anyone who plans to send you anything knows the rules and guidelines for mail before they get over-eager and start boxing you up a care package full of cookies!
The postcard mentions something I haven't brought up on here - the Red Cross. Your immediate family needs to be aware of how to contact you throughout your military career, if an emergency comes up. If you're on duty and an immediate family member dies/is dying or a spouse has a child, you can send a message to your military member through the chain of command by contacting the Red Cross. This is typically the only way that the chain of command will verify that this information is accurate and then potentially authorize the member for emergency leave. Don't expect to have your spouse home from BMT for a child birth, however, if a parent, sibling, or spouse dies, they may be granted emergency leave to fly home for the funeral. Give a few close relatives this information and the number for their local Red Cross. I passed this info on to my father and my husband, in case something happened to one or the other. Active Duty, find more information here; National Guard/Reserve, find more information here.