Outlook 2013's offline mode turns off automatic send and receive operations, letting you catch up on your old emails without an Internet connection. Usually, getting back online takes only a second click of the "Work Offline" button. Even if you get unexpectedly disconnected due to network issues, toggling "Work Offline" on and off often fixes the problem. If you get disconnected repeatedly from an Outlook.com account at work, however, you might need to change your settings to prevent the connection from timing out between send/receive events.
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Switch to Working Online
Verify that your computer is online by mousing over the network connection status in the taskbar. You might need to open the hidden icons section to find the network status.
Check whether Outlook displays a Working Offline or Disconnected notice at the bottom of the window. Working Offline indicates that Outlook is set to run offline, while Disconnected indicates a network issue. In either case, open the "Send/Receive" tab.
If Outlook doesn't show either of these messages, Outlook is already in online mode -- the email server might just be running slowly, or the program could be frozen.
Click "Work Offline" to disable offline mode and go back online. If the "Work Offline" button isn't enabled and highlighted, and Outlook's status reads "Disconnected," click "Work Offline" twice to try reconnecting.
If Outlook still won't connect, try loading your email through the Web interface, if it has one -- if the email server is down, you won't be able to get online in Outlook or reach the Web interface until it comes back up.
Prevent Disconnects from Workplace Outlook.com Accounts
Open "Send/Receive Groups" on the Send/Receive tab and click "Define Send/Receive Groups."
Lower the delay between automatic send/receive events. If you know how long your network allows an inactive connection before timing out, make sure the delay is less than that time. If not, try to progressively lower values until you stop being disconnected. Use the option in the Setting for Group area, not the When Outlook is Offline area.
Disable "Work Offline" -- or toggle it on and off, if it already appears disabled -- to reconnect. If you continue to get disconnected regardless of the value you choose, use this Fix It tool on Microsoft's site to attempt a fix by editing the Windows Registry.