Exchange 2016 mail flow rule sending email but, ???question marks appear instead of arabic

I have added a rule to block users from sending mail to any outside mail service like Outlook, Gmail,Yahoo, etc.

The rule I applied sends an email to the sender, notifying that mail cannot be sent outside the organization, but the message is in Arabic.

It does sent the email but the Arabic text is not visible and shows question marks instead.

At the bottom of the mail is written : Content-Transfer-Encoding: binary.

So is this the issue?

How to change the encoding ??

Note: I am using OWA (Webiste) to log in to the account and not any mail client like outlook 2016, etc.