Volume 30 Issue 20

Issue Date: June 12, 2025 « Previous Issue | Next Issue »

The following articles were included in our Exchange Messaging Outlook (EMO) newsletter published on June 12, 2025.

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Today's Highlights »

Prevent users from adding PST files to Outlook
Copilot in Classic Outlook
Copilot in New Outlook
Warning: Call Microsoft Support scam
Missing COM Add-ins in Classic Outlook

Prevent users from adding PST files to Outlook

An admin wanted to know how to block users from opening PST files in new Outlook.

This is controlled using an OWA mailbox policy, not client side configuration (as in classic Outlook).

The default configuration allows new Outlook clients to open PST files; the administrator needs to change the setting for OutlookDataFile to Deny.

To block PST access, run the Set-OWAMailboxPolicy cmdlet to update the OutlookDataFile setting to deny:
Set-OwaMailboxPolicy -Identity [policy name] -OutlookDataFile Deny

If you want to allow users to open old PST files but not move new mail into it, use NoExportNoGrow instead of Deny:
Set-OwaMailboxPolicy -Identity [policy name] -OutlookDataFile NoExportNoGrow

Once the policy is changed, it can take between one and twenty fours hours before the policy is applied to a specific user. If you need to block some users from using files but allow others, you can create multiple policies and apply them to different users.

Valid values for OutlookDataFile are:
• Allow: This is the default value. Users can open .pst files, import from or export to a .pst file, and copy items to and from .pst files.
• NoExport: Users can't export to a .pst file.
• NoExportNoGrow: Users can't export to a .pst file, or copy items to a .pst file.
• NoExportNoOpen: Users can't export to a .pst file, or open new .pst files.
• NoExportNoOpenNoGrow: Users can't export or copy items to a .pst file and cannot open new .pst files.
• Deny: Users can't use .pst files in new Outlook. This includes opening new .pst files, importing from or exporting to a .pst file, or copying items to and from .pst files.

For more information and other settings available, see OwaMailboxPolicy Set-OwaMailboxPolicy (ExchangePowerShell) | Microsoft Learn

Note that any changes you make will apply to both Outlook on the web and new Outlook, if supported. (PST files are not supported in Outlook on the web but other poilcy options are.)

If you want to block users from opening PST files in classic Outlook, use group policy or set a registry key value named disablepst.

HKEY_CURRENT_USER > Software > Policies > Microsoft > office > 16.0 > outlook
DWORD: disablepst
Value: 1

Prevent users from adding email accounts to Outlook

Use a Policy to Control Pst Files in Outlook | Microsoft Learn

Copilot in Classic Outlook

A user with a Microsoft 365 Personal subscription asked if copilot is available in classic Outlook. They have it in new Outlook but could not find it in classic Outlook.

Yes, Copilot is available in classic Outlook. You should have a Summarize button at the top right of email threads and Copilot prompts in the body when composing a message. The colorful Copilot button is on the message ribbon when composing a new message.

Copilot in New Outlook

Microsoft has expanded the ability to use Copilot in new Outlook. As long as you have an account in new Outlook that has a Microsoft 365 Personal or Family subscription, you can use the Copilot credits (or Copilot Pro) with other Microsoft personal accounts (outlook.com, hotmail, live, msn) or Gmail, Yahoo, and icloud in your profile. Other IMAP accounts in my profile do not have copilot.

Note that only the Family subscriber has Copilot credits, the accounts using the Family share do not receive Copilot credits.

Work or School accounts with a Copilot license will have copilot available to other personal accounts in the same new Outlook profile. Other business or school accounts in the profile need their own Copilot licenses.

Sharing Copilot in Outlook

Warning: Call Microsoft Support scam

I’ve had a couple of clients and my husband have a “Windows Defender Security Center” alert saying “access to this PC has been blocked for security reasons” and to “call us immediately” pop up while they were browsing legitimate web sites.

The window looks legit and the message is ominous, a man talking and telling the user to call the “Microsoft Support” support number on the screen immediately and not to shut down the computer. Then an alert starts beeping.

It’s a scam. Versions of this scam have been around forever but maybe it’s the Defender screen, or the man talking, or the beeping, but it seems to invoke more panic in users.

If it comes up on your computer:
Close the browser (or reboot).
Do not click links in the message.
Do not call the number.
If you call the number, do not allow them to remote into your computer to “fix” it.

Closing the browser should get rid of it then empty the browser cache in the browser settings.

However, if you have the browser set to reopen the pages you have open, it will come back when you reopen the browser. You’ll need to clear the browser cache before you can use the browser.

If you need to manually delete the cache in Edge, open File Explorer and go to %localappdata% > Microsoft > Edge > User Data > Default > Cache. Delete the folder named Cache_Data and restart the browser.

To delete the cache in Chrome, open file Explorer and go to %localappdata% > Google > Chrome > User Data > Default > Cache and delete the folder named Cache_Data. Then restart the browser.

If you want to check your settings, Edge you’ll find the “Open tabs from the previous session” in “Start, home, and new tab page”, while in Chrome the page is “On Start”.

Missing COM Add-ins in Classic Outlook

When you open classic Outlook’s File > Options > Add-ins to view COM add-ins, each section may say “ No Application Add-ins” and the button to enable and disable add-ins in missing.

This is a bug. I don't have an ETA on when it will be fixed, but if you need to enable or disable add-ins, enable the Developer tab in File > Options > Customize ribbon. Close the Options dialog and click the COM add-ins button on the Developer tab.