Emailing to a local/shared contact or contact list in Outlook for Office 365

The first time you email to a contact list, follow these steps:

Step One: Click People on the side ribbon 

Step Two: Find the local contact/group/list in the left bar

Step Three: In the right pane, there is a mail icon (an envelope) just below the name on the right hand side. Click that.

Step Four: This will launch an email to the group chosen.

Step Five: On all subsequent mailing uses, just start typing the group's name and it will auto resolve in the email being sent.