How to use Sendmail attachment as Insert as Text to display Body as Summary Format

You might have to use CDO here. This is what we do... 

More details here -

https://support.smartbear.com/testcomplete/docs/scripting/sending-email-from-scripts.html#by-using-collaboration-data-objects-cdo

function SendEmail()
{

  var mBody = "C:\\Report.html"; // Your HTML file location
  var schema, mConfig, mMessage;  

  var cdoSendUsingPort = 2;  
  var emailSMTPServer; 		 // Your office SMTP server details, will be able to get these from your System Admin.
  var smtpServerPortNumber = 25; // This should work, if not get the SMTP server port details as well
  var smtpAuthentication = 1;

  try
  {
    schema = "http://schemas.microsoft.com/cdo/configuration/";

    mConfig = Sys.OleObject("CDO.Configuration");
   
    mConfig.Fields.Item(schema + "sendusing") = cdoSendUsingPort; 
    mConfig.Fields.Item(schema + "smtpserver") = emailSMTPServer; 
    mConfig.Fields.Item(schema + "smtpserverport") = smtpServerPortNumber; 
    mConfig.Fields.Item(schema + "smtpauthenticate") = smtpAuthentication; 

    // mConfig.Fields.Item(schema + "sendusername") = ""; // User name (if needed)
    // mConfig.Fields.Item(schema + "sendpassword") = ""; // User password (if needed)

    mConfig.Fields.Update();

    mMessage = Sys.OleObject("CDO.Message");
    mMessage.Configuration = mConfig;

    mMessage.From = <enter EmailSender details>;
    mMessage.To = <enter EmailRecipients details>;
    mMessage.Cc = <enter EmailCCRecipents details>;
    mMessage.Subject = <enter Email Subject details>;

    var str = aqFile.ReadWholeTextFile(mBody, aqFile.ctANSI);
    
    mMessage.HTMLBody = str;
    mMessage.Send();

    Log.Message("Message was  sent successfully.");
    return true;

  }
  catch (exception)
  {
    TestLog.Warning("E-mail cannot be sent", exception.description);
    return false;
  }

}