This issue applicable for newer version – Outlook 2016, Outlook 2013

Some user is having failure to send and receive email in Outlook due to the email has been disconnected to the server. It can be determined by status bar at the bottom of your Outlook window whether it shows “DISCONNECTED” or “Working Offline”.

These steps will return Outlook to Online mode.

In Outlook, on the Send/Receive tab, choose Work Offline to reconnect.

Notes:

• If the background of the Work Offline button is shaded (as shown in the image above), you're not connected. But if the background is clear, you are connected.

Here are some suggested ways to reconnect to Outlook.

1.    Reset the Work Offline status

On the Send/Receive tab, choose Work Offline, and check your status bar at the bottom of Outlook window. If the status shows Working Offline, repeat the action until the status changes to connected.

2.    Check for update

i)     Go to File > Account (or Office Account if you opened Outlook).

ii)    Under Product Information, choose Update Options > Update Now.

iii)   Close the "You're up to date!" window after Office is done checking for and installing updates.

Notes:

• You may check on Update availability from any Office application such as Word, Excel, PowerPoint and so on.

There can be different reasons why you're disconnected from Outlook. These are just a few examples of some of the possible reasons.

• If your Internet connection is working, there might be a problem with the mail server.
• If you can log onto your email from a website or webmail—check to see whether you can receive and send email that way. If email isn’t working on the website, call your technical support for your email service provider for help.
• If you can send and receive mail on the website, then your mail server is fine. But your computer might need updates or there might be a problem with your account settings.