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

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?
Tech ManInformation TechnologyAsked:
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

JohnBusiness Consultant (Owner)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 TechnologyAuthor 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)Commented:
Possibly - ask clients to look at the link and change their end to see if that works.
Price Your IT Services for Profit

Managed service contracts are great - when they're making you money. Yes, you’re getting paid monthly, but is it actually profitable? Learn to calculate your hourly overhead burden so you can master your IT services pricing strategy.

Tech ManInformation TechnologyAuthor 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)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.
Tech ManInformation TechnologyAuthor 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

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Exchange

From novice to tech pro — start learning today.