Article ID: 2852113 - View products that this article applies to.
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PROBLEM

When Office 365 users try to open or view attachments in email messages in Outlook Web App, they experience the following symptoms:
  • In Office 365, the attachment isn't displayed in the message. Instead, a generic placeholder, such as “1 Attachment” is displayed, and this can't be opened.
  • When users try to view attachments in Office 365, they receive the following error message: 
    Access to attachments has been blocked. Blocked attachments: <FileName>.

CAUSE

This issue occurs if the attachment is blocked by Outlook Web App. By default, Outlook Web App blocks attachments that have the following file name extensions:
File name extension
.vsmacros.msh2xml.msh1xml.ps2xml.ps1xml.mshxml.gadget
.mhtml.psc2.psc1.msh2.msh1.aspx.wsh
.wsf.wsc.vsw.vst.vss.vbs.vbe
.url.tmp.shs.shb.sct.scr.scf
.reg.pst.ps2.ps1.prg.prf.plg
.pif.pcd.ops.mst.msp.msi.msh
.msc.mht.mdz.mdw.mdt.mde.mdb
.mda.maw.mav.mau.mat.mas.mar
.maq.mam.mag.maf.mad.lnk.ksh
.jse.its.isp.ins.inf.htc.hta
.hlp.fxp.exe.der.csh.crt.cpl
.com.cmd.chm.cer.bat.bas.asx
.asp.app.adp.ade.ws.vb.js
.xml

SOLUTION

Change the Outlook Web App mailbox policy to include and exclude the file types that you want. For more information about how to do this, see the “Add or remove file types from file access lists” section of the following Microsoft website:
View and customize settings in Outlook Web App mailbox policies
The following is an example of the Windows PowerShell commands to remove the .xml file type from the BlockedFileTypes and BlockedMimeTypes lists and add it to the AllowedFileTypes and AllowedMimeTypes lists:
Get-OwaMailboxPolicy | Set-OwaMailboxPolicy -BlockedFileTypes @{Remove = ".xml"}
Get-OwaMailboxPolicy | Set-OwaMailboxPolicy -AllowedFileTypes @{Add = ".xml"}
Get-OwaMailboxPolicy | Set-OwaMailboxPolicy -BlockedMimeTypes @{Remove = "text/xml", "application/xml”}
Get-OwaMailboxPolicy | Set-OwaMailboxPolicy –AllowedMimeTypes @{Add = "text/xml", "application/xml”}
Things to consider:
  • It may take several minutes before changes to the Outlook Web App policy take effect.
  • Be aware that by changing the Outlook Web App mailbox policy to include file types that are blocked by default, you may make your system more vulnerable to security threats.

WORKAROUND

Direct users to compress the files that they intend to send (for example, as a .zip file) and then send the compressed files as attachments.

MORE INFORMATION

Still need help? Go to the Office 365 Community website.

Properties

Article ID: 2852113 - Last Review: July 9, 2014 - Revision: 4.0
Applies to
  • Microsoft Exchange Online
Keywords: 
o365 o365a o365e o365p o365m o365022013 KB2852113

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