Office 365 Directory Based Edge Blocking support for on-premises Mail Enabled Public Folders

Hello,

I do not have a hybrid environment nor do I use Azure AD Connect tool. In my Exchange Online environment, I created a few mail enabled public folders and I receive the message above. 

The workaround is pretty clear though unacceptable:

1. add a new mail address using the custom domain being part of the mail address for the MEPF

2. run following command Set-MailPublicFolder -Identity “\Public Folders\” -EmailAddressPolicyEnabled $False

3. ensure the custom domain being part of primary SMTP address for the MEPF is configured to be the primary reply address for the MEPF

4. configure the authorative custom domain to act as a relay domain

This however exposes the Exchange Online environment to a security breach. 

When is Microsoft going to resolve this issue? The workaround to create a new contact with same proxy address does not work because the address is no longer considered to be unique.

Thanks.