For the normal Outlook users, the Sensitivity level doesn't stop recipients from taking any actions on a message. People who receive your email can take any action on the message that they want to, such as forwarding a confidential message to another person.
So actually Sensitivity Label means nothing except the recipients receive the message with a prompt:
Since you mentioned unified labelling, I assume you are deploying Microsoft 365 now, then it is another thing.
But it's Exchange online/Outlook forum here, we are not professional in Microsoft 365 area, this forum may provide you with better support: azure-information-protection
Read these docs and you should have a better understanding then:
https://learn.microsoft.com/en-us/microsoft-365/compliance/sensitivity-labels?view=o365-worldwide
https://learn.microsoft.com/en-us/microsoft-365/compliance/encryption-sensitivity-labels?view=o365-worldwide
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