Outlook can be used even when you’re not connected to the internet using ‘Offline mode’. In the ‘Offline mode’, you can perform tasks such as read and compose email messages, edit your calendar and contacts etc. This mode is particularly useful when you are traveling or when you have limited internet connectivity.
Working ‘Offline’ in Outlook is possible with the help of files called ‘OST’. They store a copy of the information on the server on your local computer. This information is what allows Outlook to be used without Internet connection. Once internet connectivity is established, the OST file synchronizes with data on the server mailbox.
Error – ‘Cannot open Outlook when Offline’
Although Offline mode is useful, some users complain about issues when using it. This article focuses on a common error about ‘Outlook not starting when Offline’ and potential solutions. The error reads:
‘Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. The operation cannot be performed because the connection to the server is offline’.
Before we go into solutions for the error, an important point to consider is that this situation mostly occurs when you are offline and try to start Outlook. It is not seen when you already have Outlook open and switch to offline mode.
Solution 1: Uncheck Favourites in Mail Navigation
Usually, when your folders are on your favorites list (mainly IMAP folders), Outlook waits for the server to be connected and thus create problems when Outlook is ‘Offline’. To resolve this, turn ‘OFF’ Favourites on your Email navigation.
To do so, go to ‘View’ menu and uncheck ‘Favourites’ in the folder pane. This helps resolve your issue in some cases.
Solution 2: Re-create OST file
Sometimes, if your OST file is damaged, Outlook may have issues working in Offline mode. To resolve Outlook error, you can delete the old .ost file and re-create the file. To delete the old .ost file, follow the steps below.
- Close Outlook and open ‘Run’ by pressing ‘Windows + R’ keys
- Then type ‘%LOCALAPPDATA%\Microsoft\Outlook\’ and hit ‘Enter’
- Select the ‘.ost’ file and hit ‘Delete’ to delete the file
Once you have deleted the old.ost file, you can create a new OST file easily by following the steps below.
- Go to ‘File’ menu and click on ‘Info’
- Select ‘Account Settings’ > ‘Microsoft Exchange’ > ‘Settings’
- Click on ‘More Settings’ and choose ‘Advanced Tab’ > ‘Offline folder file settings’
- Choose a destination to save your OST file and choose ‘Ok’.
- If you receive an error ‘.ost file couldn’t be found. Would you like to re-create it’? Click ‘Yes’ and proceed.
This will create a new OST file. Now restart ‘Outlook’ and check if the issue is resolved.
However, if you do not want to go through the hassle of deleting your old .ost file and re-creating a new one, you can use OST to PST converter. This will help you repair OST file and convert it to PST. After conversion, all Outlook items such as emails, contacts, calendars etc. will be saved to the new PST file.
The software is designed to work with all versions of Outlook including Outlook 2016. It can be used to repair .ost files that are damaged due to synchronization issues or due to hardware or software errors in only a few clicks.
Avoid corruption in .ost files
To avoid corruption in .ost files, make sure you terminate Outlook properly. Also, make sure you don’t try syncing files with the server when the internet connection is too slow. Make sure the .ost file is within the size limit to avoid any corruption or damage. Additionally, if you have been dealing with large-sized PST file issues. Click to learn how to fix a pst file that is too large.
Senior Editor, Content Analyst and a fan of exceptional customer service. John develops and publishes instructional and informational content regarding partition management, Windows hot-fixes, data management and computer troubleshooting.
As a tenured data recovery specialist, John shares exceptional insights and blog posts about data loss and data recovery across any storage device. With 8+ years’ experience in writing for Data Recovery for both Mac OS and Windows OS computers, he is an avid learner who always wants to polish and simplify the data recovery process. John passes his free time playing Chess and reading Science Fiction novels.