Winmail.dat attachment in message when sending mail from Outlook 2010, 2013 through Exchange 2016

Question

Good afternoon.

I am using Exchange 2013 (domain1) and Exchange 2016 CU23 (domain2) servers and Outlook 2010 and 2013 clients.

When I send an email to Internet mail, e.g. ...@gmail.com from Outlook 2010 on behalf of an account that has a mailbox on Exchange 2013, mail to ...@gmail.com arrives fine.

When I send an email to ...@gmail.com from the same Outlook 2010 on behalf of an account that has a mailbox on Exchange 2016, mail to ...@gmail.com comes with a winmail.dat attachment.

The situation is similar with Outlook 2013.

Two accounts are connected in an Outlook 2013 profile (one mailbox on Exchange 2013, the second mailbox on Exchange 2016)

If by default Outlook 2013 has a mailbox account set to Exchange 2013, then:

When I send an email to ...@gmail.com from Outlook 2013 on behalf of an account that has a mailbox on Exchange 2013, mail to ...@gmail.com arrives fine.

When I send an email to ...@gmail.com from the same Outlook 2013 about an account name that has a mailbox on Exchange 2016, mail to ...@gmail.com comes with a winmail.dat attachment.

If by default in Outlook 2013 an account with a mailbox is set to Exchange 2016, then mail always arrives at ...@gmail.com without the winmail.dat attachment

All the recommendations that I found on the Internet did not help:

Disable TNEF in regisrty HKEY_CURRENT_USER \ Software \ Microsoft \ Office \ 14.0 (15.0) \ Outlook \ Preferences

Answer 1

Hi @Павел Павел,

Is it possible to disable THEF on all external domains at once? Can disabling THEF lead to errors in receiving messages for external domains?

To disable TNEF on all external domains, you can run the following command:

Set-RemoteDomain Default -TNEFEnabled $false

I haven't seen it mentioned in any official document about the risks of disabling TNEF, nor did I see any reports of errors caused by it in this case. However, normally it's not recommended to modify the default configuration. And per my research, some Outlook features like voting buttons might not work properly when TNEF is disabled. See the discussion in the following link:

Any reason to keep TNEF enabled?
(Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.)

So taken in the round, personally I would suggest just disabling TNEF on certain remote domains that you are having issues with.

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Answer 2

Check the remote domain settings on the 2013 server ( domain1)

if there is a remote domain defined for domain2, ensure it has TNEF (rich text) enabled for all messages. If there is not a remote domain for domain2 configured on the 2013 server , create it:

https://learn.microsoft.com/en-us/exchange/mail-flow/content-conversion/tnef-conversion?view=exchserver-2019#tnef-conversion-options-for-remote-domains