I can't just check for and toss anything with the in-reply-to header, as if it's a reply to something that this address hasn't seen yet, it needs to be accepted.

我不能只是检查和折腾什么的在回复标题，因为如果它是一个东西，这个地址还没有见过的回复，它需要被接受。

youdao

When the service provider is ready to send the response, it USES the reply-to address from the SOAP: Header of the request message.

当服务提供者准备发送响应时，使用SOAP中的reply - to地址：请求消息的报头。

youdao

As Apple is using the reply-to address of a message's User Data Header to identify the origin rather than the raw source, receiving iPhone owners risk being fooled by a phishing attack (or just a dishonest acquaintance) that poses as a contact or a company.

ENGADGET: iPhone reportedly vulnerable to text message spoofing flaw