JMAIL发送邮件时注意的问题

最近使用jmail发送邮件，写了下面一段代码:

String recipients = "a@163.com;b@163.com";

String[] emails = recipients.split(XmlPAY.SEMICOLON);
  for (String email:emails){
   msg.addRecipient(Message.RecipientType.TO, new InternetAddress(email));

     Transport.send(msg);
  _log.debug("收件人：%s,邮件内容:%s", recipients, message);
}

结果是：a@163.com邮件收到两封邮件，收件人分别是：1) a@163.com. 2) a@163.com;b@163.com

修改代码如下：

String[] emails = recipients.split(XmlPAY.SEMICOLON);
for (String email:emails){
  msg.addRecipient(Message.RecipientType.TO, new InternetAddress(email));
}
Transport.send(msg);
_log.debug("收件人：%s,邮件内容:%s", recipients, message);

  结果正常，具体原因待分析@_@