Create Activity and associated Activity Party in Microsoft Dynamics CRM 2016 using Web API

 function CreateEmail() {
    var quoteId = Xrm.Page.data.entity.getId();
    quoteId = quoteId.replace(/[{}]/g, "");
    var OwnerLookup = Xrm.Page.getAttribute("ownerid").getValue();
    OwnerGuid = OwnerLookup[0].id;
    OwnerGuid = OwnerGuid.replace(/[{}]/g, "");
    var CustomerLookUp = Xrm.Page.getAttribute("customerid").getValue();
    var AccountId = CustomerLookUp[0].id;
    AccountId = AccountId.replace(/[{}]/g, "");

    var webapiPath = Xrm.Page.context.getClientUrl() + "/api/data/v8.0/emails";
    var email = {};
    //Lookup
    email["regardingobjectid_quote@odata.bind"] = "/quotes(" + quoteId + ")"; //Regarding is quote
    email["subject"] = "New Email";
    email["description"] = "Email Description";
    var parties = [];
    //ActivityParty (From)
    var sender = {};
    sender["partyid_systemuser@odata.bind"] = "/systemusers(" + OwnerGuid + ")";
    sender["participationtypemask"] = 1; //From

    //ActivityParty (To)
    var receiver = {};
    receiver["partyid_account@odata.bind"] = "/accounts(" + AccountId + ")";
    receiver["participationtypemask"] = 2; //To 
    //add this to collection
    parties.push(sender);
    parties.push(receiver);

    email["email_activity_parties"] = parties;

    var service = new XMLHttpRequest();
    service.open("POST", webapiPath, false);
    service.setRequestHeader("Accept", "application/json");
    service.setRequestHeader("Content-Type", "application/json; charset=utf-8");
    service.setRequestHeader("OData-MaxVersion", "4.0");
    service.setRequestHeader("OData-Version", "4.0");
    service.send(JSON.stringify(email));
    if (service.readyState == 4 /* complete */) {
        if (service.status == 204) {
            
        }
    }
}

ActivityParty entity : https://msdn.microsoft.com/en-us/library/gg328549.aspx