红帽全球峰会218.8. 标头优先于预先配置的接收者
在消息标头中指定的接收者始终优先于端点 URI 中预先配置的接收者。理念是，如果您在消息标头中提供任何接收者，即您所获得的内容。端点 URI 中预先配置的接收者被视为回退。
在下面的示例代码中，电子邮件信息被发送到 davsclaus@apache.org，因为它优先于预先配置的接收者 info@mycompany.com。端点 URI 中的任何 CC 和 BCC 设置也会被忽略，这些接收者将不会接收任何邮件。标头和预配置设置之间的选择是完全相互排除的：邮件组件需要完全从标头中接受发送者，或完全从预配置设置中接受发送者。无法混合和匹配标头和预先配置的设置。
Map<String, Object> headers = new HashMap<String, Object>();
headers.put("to", "davsclaus@apache.org");
template.sendBodyAndHeaders("smtp://admin@localhost?to=info@mycompany.com", "Hello World", headers);
Map<String, Object> headers = new HashMap<String, Object>();
headers.put("to", "davsclaus@apache.org");
template.sendBodyAndHeaders("smtp://admin@localhost?to=info@mycompany.com", "Hello World", headers);
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