Is your Microsoft 365 email not working? Your Outlook may stop sending, receiving, or syncing emails. This guide will help you confirm the problem with a few signs and learn the top reasons behind this email issue, including authentication errors, corrupted Outlook data files, full mailbox quotas, and spam filters eating your emails. You’ll also find the solutions in an order such as testing Outlook, running Microsoft Support, and rebuilding your Outlook profile. Besides, the guide also explains why email doesn’t work for some people on your team but not for others and the steps to prevent this issue in the future.