how to unblock unsafe attachments outlook

How to Unblock Unsafe Attachments in Outlook?


By default, Outlook blocks access to potentially unsafe files in an attachment (these are executable files and script files such as .exe, .vbs, .bat, .msi, ps1, etc.). Frequently used Microsoft Office files (such as doc, xlsx, ppt), text documents and files with non-standard extensions are not blocked. When you receive a mail with such an attachment, Outlook doesn’t allow you to save or view such an attachment. At the same time, in the Outlook the following message is displayed instead of an attachment:

Outlook blocked access to the following potentially unsafe attachments: Scan.001.jar

Unblock Unsafe Attachments in Outlook

Outlook blocks the following file types by default:

ADE, ADP, APP, ASP, BAS, BAT, CER, CHM, CMD, CNT, COM, CPL, CRT, CSH, DER, DIAGCAB, EXE, FXP, GADGET, GRP, HLP, HPJ, HTA, INF, INS, ISP, ITS, JAR, JNLP, JS, JSE, KSH, LNK, MAD, MAF, MAG, MAM, MAQ, MAR, MAS, MAT, MAU, MAV, MAW, MCF, MDA, MDB, MDE, MDT, MDW, MDZ, MSC, MSH, MSH1, MSH2, MSHXML, MSH1XML, MSH2XML, MSI, MSP, MST, MSU, OPS, OSD, PCD, PIF, PL, PLG, PRF, PRG, PRINTEREXPORT, PS1, PS1XML, PS2, PS2XML, PSC1, PSC2, PSD1, PSDM1, PST, REG, SCF, SCR, SCT, SHB, SHS, THEME, TMP, URL, VB, VBE, VBP, VBS, VSMACROS, VSW, WEBPNP, WEBSITE, WS, WSC, WSF, WSH, XBAP, XLL, XNK

To open a blocked file, you can ask the sender to rename the file extension to a temporary extension that is not included in the list of blocked files and send it with a new email (for example, the file setup.exe can be renamed to setup.ex_) or pack the file into a ZIP or RAR archive.

If you trust the sender, and are confident that this file is safe, you can unblock certain types of attachment files in Outlook through the registry:

  1. Close the Outlook;
  2. Run the registry editor regedit.exe;
  3. Depending on the Outlook version, go to the one of the following registry keys:
    Outlook 2010
    [HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Security]
    Outlook 2013
    [HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Security]
    Outlook 2016
    [HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Security]
  4. Create a new key type REG_SZ with the name Level1Remove;
  5. For the Level1Remove key value, specify a list of file types to be unblocked in Outlook, separated by a semicolon, for example: .exe; .hta; .inf; .jar;Unblock Unsafe Attachments
  6. Start Outlook. Now attachments with the specified types of unsafe files are unblocked.

If you use ADMX templates to manage your Office apps, you can manage the list of safe attachments in Outlook using a policy in the following GPO editor section: User Configuration\Policies\Administrative Templates\Microsoft Outlook 2010\Security\Security Form Settings > Outlook Security Mode.

If your Outlook connects to your Microsoft Exchange server, note that the Exchange administrator can specify the types of files to be blocked.

When an attachment is blocked in OWA, a message appears:

Access to this attachment is blocked <file_name >

The list of all blocked types of file attachments can be displayed as:

Get-OwaMailboxPolicy | Select -ExpandProperty BlockedFileTypes

Unblock Unsafe Attachments Outlook

Or like this for a specific server:

Get-OwaVirtualDirectory -Identity "msgmbx1\owa (Default Web Site)" | Select -ExpandProperty BlockedFileTypes

To enable a specific type of file in OWA, start the Exchange Management Shell console and execute the commands (in this example, we will unblock the CHM files on the msgmbx1 server):

Set-OwaVirtualDirectory -Identity "msgmbx1\owa (Default Web Site)" –blockedfiletypes @{remove = '.chm'}

Set-OwaVirtualDirectory -Identity "msgmbx1\owa (Default Web Site)" –AllowedfileTypes @{add = '.chm'}

Set-OwaVirtualDirectory -Identity "msgmbx1\owa (Default Web Site)" -BlockedMimeTypes @{Remove = "text/chm", "application/chm”}

Set-OwaVirtualDirectory -Identity "msgmbx1\owa (Default Web Site)" -AllowedMimeTypes @{Add = "text/chm", "application/chm”}

Get-OwaMailboxPolicy | Set-Owamailboxpolicy –BlockedFileTypes @{remove = '.chm'}

Get-OwaMailboxPolicy | Set-Owamailboxpolicy –AllowedfileTypes @{add = '.chm'}

Get-OwaMailboxPolicy | Set-OwaMailboxPolicy -BlockedMimeTypes @{Remove = "text/chm", "application/chm”}

Get-OwaMailboxPolicy | Set-OwaMailboxPolicy –AllowedMimeTypes @{Add = "text/chm", "application/chm”}

For Office365, you only need to use the last 4 code lines.

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