After I sent 'subscribe linux-kernel' to majordomo@vger.kernel.org, I got an undelivered message, in which said: majordomo@vger.kernel.org (majordomo@vger.kernel.org) Your message wasn't delivered because the destination email system rejected your message for security or policy reasons. For example, the email address might only accept messages from certain senders, or it might not accept certain types of messages, like those larger than a specific size. Contact the recipient (by phone, for example) and work with them and their email admin to determine what policy or setting blocked your message and what you should do to make sure that future messages from you won't be rejected. For more information, see Status code 5.7.1. vger.kernel.org gave this error: Hello [40.92.4.67], for your MAIL FROM address <d...@outlook.com> policy analysis reported: Your address is not liked source for email. I searched Mail list FAQ, but still have no idea. It seems that the vger.kernel.org mail server banned my mail address.