sendgrid 批量发送邮件，收件栏只显示当前用户的方案

1. 需求：批量发送邮件，用户可能看到其他用户的邮箱地址，之前用BBC发送，但问题是接收地址是同一个。
2. 官方解决方案：https://sendgrid.kke.co.jp/docs/Tutorials/A_Transaction_Mail/send_with_substitution.html
3. 注意：最大发送数量问题
4. 在springboot2中的代码实现

private void sendMany(List<String> lstAddress, String mailFrom,String subject, String text,String API_KEY) {

try{

Email from = new Email(mailFrom);

Mail mail = new Mail();

for (String mailto : lstAddress) {
Email to = new Email(mailto);
Personalization personalization = new Personalization();
personalization.addTo(to);
personalization.addSubstitution("-name-", mailto);
mail.addPersonalization(personalization);
}

mail.setFrom(from);
mail.setSubject(subject);
Content content = new Content("text/plain", text);
mail.addContent(content);

SendGrid sg = new SendGrid(API_KEY);
Request request = new Request();

request.setMethod(Method.POST);
request.setEndpoint("mail/send");
request.setBody(mail.build());
Response response = sg.api(request);

}catch(IOException ex){

ex.printStackTrace();

}

}

mail.build()生成的JSON结构如下：

{ "to" : [ "alice@test.com", "bob@test.com" ], "sub": { "-name-": [ "アリス", "ボブ" ] }