On suspicious attachment type

You can select attachment types that you consider suspicious to be blocked. By default file names with double extensions and file types listed under the Executable and Object Code sections on the Attachment types tab are considered suspicious. You can optionally specify a size limit (if an attachment of the relevant type exceeds the limit, the attachment is blocked). You can also block potentially unwanted applications, and you can enter exceptions to that rule.
Note PureMessage for Microsoft Exchange detects the True File Type (TFT) of the attached file and therefore even if the attachment is renamed, PureMessage for Microsoft Exchange will still detect the original file type.

Click Configuration > Transport (SMTP) Scanning Policy > Content. On the Content filtering screen, in the On suspicious attachment bar, click Define. In the Suspicious attachment type dialog box, click the Attachment types tab.

In the Select attachment group drop-down, choose an attachment category.

PureMessage for Microsoft Exchange is preconfigured with a list of file types that are currently used to carry threats. Check the relevant attachment type(s) to block. You can select or clear all the options by using check box on the title bar. Optionally, enter a file size limit in MB.

Optionally, select the Block adware/potentially unwanted applications (PUAs) check box to block adware and PUAs.

If you want to allow an application that may otherwise be blocked as an adware or PUA, click Add and enter the name of an application that you want to allow. For more information about adware and PUAs that Sophos detects, go to http://www.sophos.com/en-us/threat-center/threat-analyses/adware-and-puas.aspx.

Click Edit to edit a highlighted allowed adware/PUA.

Click Remove, to remove a highlighted adware/PUA from the list of allowed applications.

Click OK to save your changes and return to the Content filtering screen.
Note From the Manage changes menu, click Save changes to save your configuration.

If you want to allow certain attachments from the suspicious attachments list, follow the steps in Exclude suspicious attachments from filtering.