AACOMAS does not have a centralized letters service.  To apply to an osteopathic medical school, search for the school name in Step 1 of the Delivery process.  Most osteopathic medical schools are Interfolio electronic receivers which means application materials sent to a secure electronic inbox accessible by the admissions staff.  Letters will never get lost in the mail, and are guaranteed to arrive according to the time table given during the delivery checkout process.