Ironport Upgrade to AsyncOS 13.0, winmail.dat attachments now accompany outbound email in HTML format (Exchange 2010)

[jyblackwood]

We just upgraded our Cisco Ironport C170 to AsyncOS 13.0.  We have an inhouse Exchange 2010 server.

Now outbound emails that are in HTML format have a winmail.dat attachment.

This attachment causes some email platforms (like Yahoo) to treat the email as dangerous because of the attachment.

How do I prevent winmail.dat attachments from being included on outbound email?  I believe they were stripped before in previous versions of AsyncOS.

Thank you.

-Jim B

[ppreenja]

Hello Jim,

Firstly, the ESA C170 appliance can't be upgraded to Async OS version 13 and hence I am not sure that how were you able to upgrade your C170 appliance to Async OS version 13.

The most common reason that Outlook will encapsulate an email in a winmail.dat file is if the message is sent with Rich Text Formatting (RTF), however, there are a variety of reasons that Outlook or Exchange may be doing this.

I would recommend you to review the outlook and exchange settings properly to ensure that it is not using this rich text format in any of the available settings.

Here is a knowledge base article which explains the reason behind this issue:

https://www.cisco.com/c/en/us/support/docs/security/email-security-appliance/200037-Troubleshooting-winmail-dat-Attachments.html

https://support.microsoft.com/en-in/help/290809/how-e-mail-message-formats-affect-internet-e-mail-messages-in-outlook

To remove the "winmail.dat" attachment from the messages, you can create an Outgoing Content Filter with the condition Attachment file info "(?i)winmail.dat" and the action Strip Attachment by file info "(?i)winmail.dat".
You can then apply the same to the desired policy under Mail Policies-->Outgoing Mail Policies.

I hope that helps.

Cheers,
Pratham