Summary
When users report that they aren't getting email, it can be frustratingly hard to find what's wrong. You might run through several troubleshooting scenarios in your mind. Is something wrong with Outlook? Is the Office 365 service down? Is there a problem with mail flow or spam filter settings? Or is the problem due to something that's entirely outside your control, like the sender is on a global block list?
Fortunately, Office 365 provides powerful automated tools that can help you find and fix a variety of problems quickly and easily.
Details
Check the Service Health Dashboard
To make sure there is no service outages, check the Office 365 Service Health Dashboard. As an Office 365 admin, you can see whether there has been a service interruption or outage in your service. The Service health page shows status information for today, the past six days, and 30 days of history.
View the status of your services
Use the Support and Recovery Assistant tool for individual users
If a user in your organization is having trouble receiving email, it could be due to a licensing issue, a profile problem, the wrong version of Outlook, or a mix of other issues. Support and Recovery Assistant for Office 365 finds and helps you fix most issues. As a first step in troubleshooting email delivery problems for Office 365 for business, we recommend that you download and run Support and Recovery Assistant on the affected machine:
Microsoft Support and Recovery Assistant for Office 365
Use administrator tools to fix email delivery problems
If the Support and Recovery Assistant tool doesn't resolve the issue, you can run the Mail Flow Troubleshooter tool as an Admin. You'll answer a few questions, and then the tool will scan your Office 365 configuration to help identify mail flow issues in your environment.