Problem

The client had an Exchange 2010 environment with 2008 R2 DC’s , some of the users were complaining that every now and then they get Winmail.dat attachments and the Issue affects both Outlook and OWA users

Troubleshooting

After extensive troubleshooting we found out that there was a Firewall/ SMTP Gateway Watch Guard XTM device in place to receive the emails and it was striping out the header of the email that identify it as Rich Text formatted.  This header is needed by the outlook client to interpret the winmail.dat attachment. When the email client cannot read the proper formatting of the email, it displays the attachment as a winmail.dat file

Resolution

Before running towards the solution or editing the config of the SMTP gateway , it would be best to probably bypass the gateway and forward port 25 (TCP) directly towards the Hub Transport server, than test the issue again to see if its resolve.  As now if are not getting the winmail.dat attachment and are receiving the emails fine then we can be sure its the SMTP gateway issue.

In our case, we made changes to SMTP-proxy on the Watch Guard to allow the header of type •X-MS-Has-Attach:* 
•X-MS-TNEF-Correlator:* 
•X-MimeOLE:* through the SMTP proxy.You may have to make similar changes to what ever SMTP gateway you have.

Hope this helps you to fix the issue in hand, for more visit our support options here

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An automobile enthusiast at heart and computer geek by profession, started my Career with MS in 2005.Left Jobs and started Pledge Technologies (the parent company to Grishbi) back in 2009.We have been providing IT consulting to various Small and Medium businesses across US and UK since then.Our company specialises in Microsoft Server technologies like AD, Exchange, the rest and with numerous Office 365 migrations under our belt, we quite an expert with that too. Whatever we learn in our day to day life, we share it back on Grishbi as a Thank for all the love and support our customers have given us.
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