What HML merge field should be included in an email to allow prospects to manage...

The HML merge field that should be included in an email to allow prospects to manage their email preferences is {{OptOut}} or {{EmailPreferenceCenter}}. The {{OptOut}} merge field inserts a link that allows prospects to opt out of receiving emails from the sender. The {{EmailPreferenceCenter}} merge field inserts a link that allows prospects to choose which types of emails they want to receive from the sender. The {{Unsubscribe}} merge field is not valid in HML, as it is only used in PML. The {{ReportSpam}} merge field is not recommended, as it can negatively affect the sender’s reputation. The {{Opt_Out}} merge field is not valid in HML, as it uses an underscore instead of a camel case1. References: 1: HML Merge Fields