With a Microsoft Exchange Server or Office 365 account, you can work offline to avoid connection charges or stop Outlook from attempting to send and receive messages over a slow network connection.
But outlook.com provides you the facility to work offline also.
How to Switch between Working Offline and Working Online in Microsoft Office 2016, 2013, 2010?
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Click Send / Receive > Work Offline.
You know you’re working disconnected when Work Offline is featured on the strip or Working Offline shows up on the status bar at the base of the Outlook window.
When you’re prepared to work online once more, click Send/Receive > Work Offline.
The catch content doesn’t change, however it’s just featured when you’re working disconnected. Working Offline on the status bar likewise leaves when you’re working on the web.
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How to Change : How Much Mail to Keep Offline?
Click File > Account Settings > Account Settings.
Select an Exchange account, and then click Change.
Under Offline Settings, move the slider to the desired amount of time, such as All, 12 months, 6 months, 3 months, or 1 month.
For more details, visit : www.office.com/setup