The SMTP service of IIS keeps sending emails as soon as it is started.

Recently, a strange problem was found on a test server. As long as the SMTP service of IIS is started, it starts to send out mails automatically and frantically. Reading emails and so on seems to have been maliciously attacked. No matter how you restrict SMTP permissions, it does not work. Finally, I accidentally discovered the crux of the problem. There is a queue directory under the SMTP service working directory, which contains several hundred MB *. eml files. As the name suggests, the SMTP service will read the emails from here and then send them out ...... So I killed all the files in this directory and solved the problem...