Change ‘Lookup For’ in Party list Using JavaScript

Introduction: Party list like “TO” usually contain record of type Accounts, Contacts, Knowledge Articles, Leads, Users

If you want to restrict the Lookup values, write the below script on load on the form and also on change of the partly list

var lookup = {
    dropdown: function (execContext) {
        var formContext = execContext.getFormContext();
        if (formContext.getAttribute("dropdown").getValue() != null) {
            dropdown = formContext.getAttribute("dropdown").getValue();
            var LookUpFor = ['account'];
            var fieldlist = ['to','cc','bcc'];
 fieldlist.forEach(
        function (item, index) {
            formContext.getAttribute(item).setValue(null);
            formContext.getControl(item).setEntityTypes(LookUpFor);
        });
        }
    }}

Here for each value in fieldlist, the lookup for will be set to account. This is not applicable to “FROM” as it has OOB restrictions.