Prevent a user from adding an internal email address to 'BlockedSendersAndDomains'

Good morning

When an Outlook user blocks a particular sender I can see when running the EMS command:

Get-MailboxJunkEmailConfiguration 'alias'

That the email address is added to 'BlockedSendersAndDomains' which is fine.However, a couple of users have blocked emails coming from important internal email addresses. This causes the email to be rejected by Exchange when it is sent.

How do I stop them from being able to block internal email addresses while still allowing them to block any other email address. Or is there an alternative way of achieving my desired goal?

Thanks in advance!