With Exchange 2003 we had to make changes to the Registry in order to allow or block particular file types in OWA, and in Exchange 2007 we had to configure OWAs’ virtual directories. Since Exchange 2010 that this is done through Outlook Web App Mailbox Policies and this applies to the latest Exchange 2013 and Exchange Online.
To check which files are currently being block, and to change this is necessary, first connect to your exchange online service via powershell.
$cred = Get-Credential
$session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.outlook.com/powershell/ -Credential $cred -Authentication Basic –AllowRedirection
Import-PSSession $session
After successfully connecting, run the following cmdlet to check what file types are being blocked:
Get-OwaMailboxPolicy "policy name" | Select -ExpandProperty BlockedFileTypes | Sort
If you want to make changes and allow certain file types, such as XML files for example, you remove the .xml 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”
Remember to ensure the settings in the ECP at permissions -> Outlook Wep App policies -> file access match those in servers -> virtual directories -> owa (Default Web Site) -> file access in terms of Direct File Access which enables or disables direct access to all file types in OWA. If this parameter is set to $False, users will not be able to click on attachments in e-mails to open or save the files. The attachment is visible, but the link is grayed out.
