If you've suddenly started receiving email from an Outlook.com group you may be wondering how you got added to that group, and perhaps how you can leave the group. When you were added you should have received a welcome email that tells you about the group, including who added you. It's possible that email may have gone into your junk email (or "spam") folder.
When you locate the welcome message you'll discover who added you, what the group is about, and you'll find a link to leave the group if you'd rather not be a member.