Cannot Open Default Email Folder –Outlook.ost is not an Offline Folder File

admin | May 20th, 2016 | Outlook

MS Outlook uses OST files when Outlook account is configured with Exchange server by enabling MAPI Protocol. An OST file lets user work in offline mode and any changes made are updated when it is synchronized with Exchange Server. Sometimes, user may encounter issues while starting Outlook that displays with an error message ‘Cannot Open Default Email Folder –Outlook.ost is not an Offline Folder File’. The blog will be discussing the same error, its causes, and its possible solutions to overcome the error.

Causes of the Error

This error mainly occurs due to two reasons firstly, when the OST file is damaged/corrupt and it cannot be recognized by Outlook, and secondly, when MS Outlook cannot access the associated Exchange Server mailbox & causes synchronization issues between Exchange mailbox offline folders with system OST file.

Issues leading to such situation are as follows:

– Improper setup of the email account in Outlook for accessing the Exchange mailbox

– Deletion of email account for Exchange mailbox on Outlook

– Accidental Deletion of mailbox on MS Exchange Server

– Interrupted Power Shutdown during Synchronization

– Virus Attack can make OST file corrupted & inaccessible

– Improper settings while mapping Outlook email client to Exchange mailbox

How to resolve the Error

In order to troubleshoot the error, Users need to check if the Exchange mailbox & email account are valid or not.

– If Exchange mailbox & Outlook email account are valid

User needs to ensure that email account settings in Outlook are correct and Outlook can be connected to its Exchange Server correctly. Restart the Outlook and check send/receive your emails on the Exchange Mailbox. It will make MS Outlook create a new OST file automatically & synchronize its data with the Exchange Mailbox.

– If Exchange mailbox or email account does not exist

User needs to delete the current mail profile and re-create a new one following the steps stated below:

  1. Go to Start and click on Control Panel
  2. Search the control panel items and double-click on Mail
  3. A mail setup dialog box will be opened and click on Show Profiles
  4. Select the incorrect profile from the list of profiles and click on Remove to remove it
  5. Repeat the procedure until all the incorrect profiles have been deleted
  6. Click Add to create a new profile and add email account according to the type
  7. Restart MS Outlook and it will run smoothly without any error

The above method may work in some situations helping users delete the incorrect profile and creating a new one. However, this approach will not help if the Outlook OST file is highly corrupted and it may lead to permanent loss of data. Another effective solution is to use a third party tool, OST to PST Conversion to scan the OST file of any state and recover data into healthy PST file. The software can be used to recover data from the corrupted/ inaccessible or orphaned OST file, keeping the original formatting of the data items intact after recovery. It has ability to save the recovered data in different featured file formats like EML, PST, and MSG. The contents of the damaged OST file can be easily accessed in any MS Outlook application after restoration.


In the blog, we have discussed about one of the most common error encountered in MS Outlook while starting Outlook that displays with an error message ‘Cannot Open Default Email Folder –Outlook.ost is not an Offline Folder File’. The main causes of the error have been described along with the situations that could lead to generation of error. The blog further describes the solution on how to resolve the same error.