Above the communication protocols are the optional file attachment and security layers that are implemented with MIME.

通信协议的上面是可选的文件附件和安全层，用MIME实现。

youdao

Above the communication protocols are the optional file attachment and security layers that are implemented with MIME.

通信协议的上面是可选的文件附件和安全层，用MIME实现。

youdao