Backing up Office 365 .OST files necessary?

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Our small office recently switched our MS Office 365 email accounts from POP/SMTP to online Exchange, continuing to use Outlook Desktop client for email.  Had the existing PST files in documents subdirectory OUTLOOK, which are being backed up every night.  Now see that new email is now stored in

C:\Users\USER\AppData\Local\Microsoft\Outlook

in an OST file.  I originally modified our backup routines to include this subdirectory as well, but coming to the realization that there may not be any point to backing up these OST files in this manner, as not sure that could do anything with this OST file for recovery.  So two questions:  one, am I correct in no point in backing up the OST files now that the email is online; and two, what is preferred method to backing up online Exchange emails (exporting to PST file, etc.?)  Thanks for any guidance.

 

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Simple answer = yes, back up the OST files. Why?

While the emails are kept in the Exchange server, they will be there for only a short time period set by the manager of the Exchange software. Some companies will cut the time limit to only emails received within the last two weeks, otherwise they would accumulate so many emails that it would bog the system down keeping track of all of them. If you want to keep an email longer than the Exchange server will, then you have to save that email on your PC. These saved emails will be saved in that OST file. After your Exchange server’s keep time period, that OST file will be the only copy of those older emails.

You can backup the OST file by copying it when Outlook is closed. The method I use to backup is automatic archiving of the emails in the OST file. The archived file will always be a PST file which is way easier to work with than an OST file (can be used on Outlook that is not connected to an Exchange server to open and extract the email you want).

I like to suggest you create a rule or settings that keeps all the emails you send. Sometimes you need to remind yourself what you emailed them earlier.

HTH, Dana:))

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windbg

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As I understand it, OST is a cache, PST is the mail store. Backing up an OST has no real value.
https://support.microsoft.com/en-us/office/introduction-to-outlook-data-files-pst-and-ost-222eaf92-a995-45d9-bde2-f331f60e2790

cheers, Paul

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Paul T wrote:

As I understand it, OST is a cache, PST is the mail store. Backing up an OST has no real value.

From the link you provided:

Offline Outlook Data File (.ost)
Most other account types, such as IMAP accounts, Microsoft 365 accounts, Exchange accounts, and Outlook.com accounts use an Offline Outlook Data File (.ost) file to store a synchronized copy of your mailbox information on your local computer. When your connection to the mail server is interrupted, for example, when you’re on an airplane without WiFi or if your internet connection disconnects, you can still access all emails, calendar data, contacts, and tasks that have been previously downloaded.

True, you permanently save the emails locally with a PST file, but backing up the OST saves the emails you haven’t saved that are still in the cache. A bigger reason to backup the OST file is that it can become corrupted which will prevent connecting to the Exchange server.

The following link to SysTools (modified August 2022):
https://www.systoolsgroup.com/updates/backup-ost-file-outlook-exchange/
States these reasons to back up the OST file:

OST Synchronization Problem: A user can work with OST files in offline mode. But, it is not possible when it is about Exchange Server. So, when Outlook is synchronized with the Exchange Server, it becomes difficult to work on the file. That is why it is needed to backup OST files.

Authentication Issue: To access the data on Exchange Server, proper credentials along with the validation are required. To avoid all the complex procedures, it is better to archive the OST file.

Data Recovery: In case of accidental file deletion, file corruption, or highly damaged OST files, the data cannot be accessed. So, to make data available, it is recommended to make a backup of the offline .ost files for the accounts.

OST Corruption: Due to virus attacks, abrupt shutdown, and other software-related issues, the OST file becomes out of reach and its data cannot be availed. So, just to rely on the OST file is a mistake. Hence, it is necessary to back up the Offline OST files.

The web page also explains various ways to back up the OST file.

Like all backups it is only important when you need a backup copy.

That being said, if you backup the entire PC then backing up the OST separately is not necessary as the OST file will be in the total backup.

I have been involved in a corrupt OST file and a backup was way easier to restore than trying to repair the OST with some expensive 3 party software. So, from experience I think the OST backup had a lot of value.

HTH, Dana:))

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windbg

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If you delete the OST, the mail client will download all the mail again.
Up to you if a restore or full download is better.

cheers, Paul

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Download “all the mail again”.  Even if it’s been in a folder for several months? Or longer?  I understood that online servers cannot possibly keep all mail belonging to all users?

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petesmst wrote:

online servers cannot possibly keep all mail belonging to all users

Why not, it’s only a bit of data and you are paying?

cheers, Paul

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