In Microsoft Outlook, you might occasionally find that it goes in to offline mode with your mail server and you stop receiving any emails. The most common cause of this is due to loss of internet while Outlook is open.
How do you know when you’re working offline or online in Outlook? There are visual cues, starting with the status bar at the bottom of your Outlook window. If either of the following status indicators are shown, it means Outlook isn’t connected to your mail server.
Outlook 2013 / 2016 / Office 365 Notification
Office 2010 Notification
Returning to an online work mode is a simple process.
Guide For Outlook 2013 / 2016 / Office 365
Guide For Outlook 2010
Still no luck? If you can use that email account with a website, such as Outlook.com, see whether you can receive and send new mail using that site. If you can’t, call your technical support or your email service provider for help.