Obtaining an ESA letter online is a simple process that might make it simpler to qualify for an emotional support animal. You may easily obtain an ESA letter with the assistance of a registered mental health practitioner. A visit with a medical or mental health expert in your state is usually the first step. An ESA Letter is a legally binding document that confirms a person's need for an emotional support animal (ESA) as part of their treatment plan for a mental or emotional disability.