When I set a name for multiple to element I got first elements name for other element.
for example:
<mail mailhost="smtp.gmail.com" 
      user="sender@gmail.com" 
      password="pass" ssl="true" 
      mailport="465" 
      subject="Test Gmail"
      charset="utf-8">

        <from  name="Sender" address="sender@gmail.com"/>
        <to name="receiver 1" address="receiver-1@yahoo.com"/>
        <to name="receiver 2" address="receiver-2@outlook.com"/>
        <header name="header name" value="header value"/>
        <message>The nightly build has completed</message>

</mail>

I got (To: receiver 1) for receiver-2@outlook.com in mail name.