req.setMethod('POST');
        req.setHeader('Content-Type', 'application/x-www-form-urlencoded');
        SendmailUtils.Emailtemplate emailtmp=new SendmailUtils.EmailTemplate();
        emailtmp.emailTemplate=bdy.escapeHtml4();
        if(Contactlists.size() == 0)
        {
            ReturnContactList([SELECT Name,FirstName,LastName,description,Email,Title,Company,ID,phone FROM Lead where email=:Emailcon LIMIT 1]);
        }
        string isQue='0';
        req.setBody('AUCode='+aucode+'&SOrgID='+ocode+'&Subject='+sbj+'&To='+too+'+&Bcc=&contacts='+JSON.serialize(Contactlists)+'&Body='+JSON.serialize(emailtmp)+'&contents='+JSON.serialize(contentCategoryIDs)+'&IsQueue='+isQue); 
      
        try {
            res = http.send(req);
     
            if (res.getBody() != null) {
                if(isQue=='0')
                {
                    List<SendmailUtils.EmailTemplateListData> emailLists=new List<SendmailUtils.EmailTemplateListData>();
                    emailLists=(List<SendmailUtils.EmailTemplateListData>)json.deserialize(res.getbody(),List<SendmailUtils.EmailTemplateListData>.class);
                    String userName = UserInfo.getUserName();
                    User activeUser = [Select Email From User where Username = : userName limit 1];
                    String userEmail = activeUser.Email;
                    for(SendmailUtils.EmailTemplateListData emailData: emailLists)
                    {
                        if(emailData.To != null || emailData.To != '')
                        {
                            Messaging.SingleEmailMessage emails = new Messaging.SingleEmailMessage(); 
                            List<String> sendTo = new List<String>();
                            sendTo.add(emailData.To);
                            // System.debug ( 'emailData.To' +emailData.To);
                            emails.setToAddresses(sendTo);
                            emails.setSubject(emailData.Subject);
                            if(emailData.Body!=null)
                            emailData.Body = emailData.Body.unescapeHtml4();
                            emails.setHtmlBody(emailData.Body);                         
                            emails.setReplyTo(userEmail);

        -----------:  Error shows in this below line:------         
   
     Messaging.SendEmailResult [] resSentEmail= Messaging.SendEmail(new Messaging.SingleEmailMessage[] {emails});  

                            for ( Messaging.sendEmailResult result : resSentEmail ) {
                                if ( !resSentEmail[0].isSuccess () ) {
                                  //  System.debug ( 'result' +result  );
                                }        
                            }