nginx可以作为不接受明文登录的后端服务器的邮件代理吗？

Nginx可以作为不接受明文登录的后端服务器的邮件代理吗？

我想知道要包含哪个指令以便调用STARTTLS / STLS,但通过IMAPS或POP3S进行通信就足够了.

nginx.conf的相关(？)部分

mail {
    auth_http           localhost:80/mailproxy/auth.php;
    proxy               on; 
    ssl_prefer_server_ciphers   on;
    ssl_protocols           TLSv1 SSLv3;
    ssl_ciphers         HIGH:!ADH:!MD5:@STRENGTH;
    ssl_session_cache       shared:TLSSL:16m;
    ssl_session_timeout     10m;
    ssl_certificate         /etc/ssl/private/hostname.crt;
    ssl_certificate_key     /etc/ssl/private/hostname.key;
    imap_capabilities  "IMAP4rev1" "UIDPLUS"; 
    server {
        protocol    imap;
        listen      143;
        starttls    on;
    }
    server {
        protocol    imap;
        listen      993;
        ssl     on;
    }
    pop3_capabilities  "TOP" "USER";
    server {
        protocol    pop3;
        listen      110;
        starttls    on;
        pop3_auth   plain;
    }
    server {
        protocol    pop3;
        listen      995;
        ssl     on;
        pop3_auth   plain;
    }
}