The roles of the director/dean of admissions vary from one school to another. The director of admissions is usually the facilitator/overseer of the admissions process and head committee meetings. The dean is higher ranked and tends to have a stronger say in admissions decisions - they sometimes have the power to break ties or overturn/approve committee decisions to offer interview. I would suggest sending update letters addressed to the "Admissions Committee" via the regular admissions email address and simply ask them to include it in your file. That will ensure that the committee will eventually read your update letter. Some schools will even place your update letter immediately into your electronic file. The dean and director of admissions are extremely busy and may overlook your email in their overcrowded in boxes. However, if you really prefer something personal, snail mail would probably be better IMO.