Office 365 (Outlook | Outlook on the web) - Send an Email to a Contact or Personal Group
You can store e-mail addresses, home and work addresses, phone and fax numbers, and other information for your contacts. Each contact (Contact: In the Address Book, a collection of information about a person that may include e-mail addresses, phone numbers, street addresses, and more.) can include information that is important to you, including birthdays, children's names, notes, and more.
Outlook on the web
Watch the below clip on how to send an email from a contact in your Outlook on the web application:
Watch the below clip on how to send an email from a contact in your Outlook 2016 desktop application: