How to add external email to Distribution list in Office 365

1. Login office 365 with your administrator account.
2. Go to Exchange admin center.
3. Navigate to recipients>contacts. Click + and select Mail contact.

4. Create a new Contact.

5. Now click on groups. Click + in New Office 365 group. Select Distribution list.

6. You have options to enter the group info, modify the ownership, and add members.

7. Save the settings.