For legal reasons, all marketing e-mails sent out must contain an Unsubscribe link that the receiver of the message can use to unsubscribe from future marketing messages.
This default link cannot be left out.
The service related to this link is provided by a third party, hence the automatic message itself that the recipient would receive once they hit the link cannot be customized.
This is the designed system behaviour.
SAP Help Centre -> SAP Hybris Cloud for Customer Administrator Guide -> E-Mail Templates -> Unsubscribe Placeholder
Unsubscribe, Unsubscribe link, E-mail unsubscription, Marketing E-mails. , KBA , AP-RC-BCT , Business Config. Tools (SAP Business ByDesign , Problem