O365 mailbox users receive Winmail.dat file from on-prem users in Hybrid setup

Tech Man
Tech Man used Ask the Experts™
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We have Hybrid environment configured a few weeks ago. Started migrating users from on-Prem to O365.
Everything was working ok for the last two weeks. This morning cloud (O365) users started complaining that they receive Winmail.dat file attachments from On-premises users. Nothing that we changed on our end.  When on-prem users send email to O365 user, winmail.dat file is getting attached. Our users have formatted signature in the body of the email.
According to some articles, the recommendation is to set MailFlow\RemoteDomains\Default\Use Rich text format to NEVER.
After making this change and waiting for a couple of hours basically nothing changed.
Any thoughts?
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JohnBusiness Consultant (Owner)
Most Valuable Expert 2012
Expert of the Year 2018

Commented:
Please see if this solution enclosed in this link works for you. A change apparently made to Exchange.

https://community.spiceworks.com/topic/1977092-contact-receiving-attachments-as-winmail-dat
Tech ManInformation Technology

Author

Commented:
I already made that change on my Office 365 admin center.
I made that change this morning but still receive Winmail.Bat file when email sent from onprem to O365.

If I am not mistaking this change has to be made on the receiving side right ?
JohnBusiness Consultant (Owner)
Most Valuable Expert 2012
Expert of the Year 2018

Commented:
Possibly - ask clients to look at the link and change their end to see if that works.
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Tech ManInformation Technology

Author

Commented:
Did not understand what link ?

Also, do you have an idea how long does it take for TNEFEnabled setting to take effect in o365?
JohnBusiness Consultant (Owner)
Most Valuable Expert 2012
Expert of the Year 2018
Commented:
This link above

https://community.spiceworks.com/topic/1977092-contact-receiving-attachments-as-winmail-dat

With regard to the second question, no. But it is now late here and the change should be in place when people show up tomorrow.
Information Technology
Commented:
John, after reading little more about TNEF, I understood that the setting must be set on the sending side not receiving.
What I did is I looked for the Remote domains that were created when I ran HCW to configure hybrid and set TNEFEnabled to $false on them.
Basically, my On-premises Exchange Server had three remote domains: One Default and two created by HSW. I set all three TNEFEnabled to $false.

>Set-RemoteDomain "Hybrid Domain - DomainName.mail.onmicrosoft.com" -TNEFEnabled $false
>Set-RemoteDomain "Hybrid Domain - DomainName.onmicrosoft.com" -TNEFEnabled $false
>Set-RemoteDomain Default -TNEFEnabled $false

Thanks

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