Appendix A: Using an Exchange Edge Transport server for attachment filtering

If you don't want to expose your Mailbox servers directly to the internet, you can use an Edge Transport server in your perimeter network. The Edge Transport server role is available in Microsoft Exchange Server 2013 Service Pack 1 (SP1) or later.

In an Exchange Edge Transport server, the Attachment Filtering agent is available by default. The agent filters out email messages based on file name and email content type. As a consequence, emails containing certain attachments may not reach PureMessage for Microsoft Exchange (and their intended recipients) in their original form. This could affect the detected viruses, content or spam score that PureMessage for Microsoft Exchange detects for that message.

The Exchange Attachment Filtering agent also performs searches inside archive files. The default list of attachment content types and file names affected is:

Content types

  • application/x-msdownload
  • message/partial
  • text/scriptlet
  • application/prg
  • application/msaccess
  • text/javascript
  • application/x-javascript
  • application/javascript
  • x-internet-signup
  • application/hta

File names

*.xnk *.wsh *.wsf *.wsc

*.vbs *.vbe *.vb *.url

*.shs *.shb *.sct *.scr

*.scf *.reg *.prg *.prf

*.pif *.pcd *.ops *.mst

*.msp *.msi *.psc2 *.psc1

*.ps2 *.ps11 *.mdb *.ps11xml

*.ps1 *.msc *.mdz *.ps1xml

*.mdw *.mdt *.mde *.ps2xml

*.mda *.lnk *.ksh *.jse

*.js *.isp *.ins *.inf

*.hta *.hlp *.fxp *.exe

*.csh *.crt *.cpl *.com

*.cmd *.chm *.bat *.bas

*.asx *.app *.adp *.ade

The Exchange Attachment Filtering agent can be configured using the Exchange Management Shell.

To view the Attachment Filtering agent configuration, use:

Get-AttachmentFilterListConfig

To view a complete list of all file name extensions and content types affected, run the following command:

Get-AttachmentFilterEntry | FL

To disable the Exchange Attachment Filtering agent, use the following command:

Disable-TransportAgent "Attachment Filtering Agent"

For more information about Attachment Filtering agent cmdlets, see Anti-spam and anti-malware cmdlets (Anti-Spam cmdlets > Attachment Filtering cmdlets on Edge Transport servers).

For more information about attachment filtering, see Attachment filtering on Edge Transport servers.