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Winmail.dat Attachments

Stewart -


My users receive winmail.dat attachments they can't open, or "application/ms-tnef" attachements.


  • On-Premise Server + WebMail Installations: Version 6.0 > Current Version
  • Webmail Only Installations: Version 6.0 > Current Version


Emails sent from Microsoft Outlook in Rich Text Format messages are sent as a bundled attachment called winmail.dat, using Transport Neutral Encapsulation Format.
If your server doesn't include support for these files you will see the winmail.dat attachments.


Adding support for TNEF files is fairly simple and just requires the installation of a package.

Installing tnef packages (required for winmail.dat format with .xlsx attachments in Atmail 7.4+):

For Ubuntu users:

# apt-get install tnef

For Centos users:

Download the latest tnef package from GitHub (Attached "tnef-1.4.11.tar.gz”)

Copy to /tmp directory in your VM and extract

# tar vxfz tnef-1.4.11.tar.gz

Go to tnef folder

# cd tnef-1.4.10

Make and install package

# ./configure
# make
# make install
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