Final answer:
Mailing out vaccine reminders is considered a part of Customer Relationship Management because it involves maintaining communication with clients to improve business relationships and customer retention.
Step-by-step explanation:
The task of mailing out vaccine reminders belongs to Customer Relationship Management (CRM). CRM involves managing the company's interaction with current and prospective customers. It employs data analysis on a customer's past interactions with a firm to strengthen commercial relationships with customers, with a particular emphasis on customer retention and ultimately generating sales growth. In the case of mailing out vaccine reminders, the task is directly related to maintaining communication with clients to ensure they are engaged and informed, which is a core function of CRM.