Thx a lot ... I do understand better now.

In my nginx.conf I do have:

*****
stream {
limit_conn_zone $binary_remote_addr zone=straddr:10m;

upstream backendmail {
server email.domain.tld:448;
}
}

*****

In my server.conf I do have:

*****
server {
listen 448 ssl;
error_log /var/log/nginx/error-proxy_mail.log debug;
ssl on;
ssl_certificate /etc/ssl/certs/cert.org.chained.crt;
ssl_certificate_key /etc/ssl/private/iRedMail.key;
include /etc/nginx/sslciphers.conf;
ssl_session_timeout 60m;
ssl_handshake_timeout 10s;
proxy_connect_timeout 10s;
proxy_timeout 300s;
proxy_pass backendmail;
limit_conn straddr 15;
limit_conn_log_level error;
}

******
When tying to run the server:

nginx: [emerg] "ssl_handshake_timeout" directive is not allowed

If removing this directive :

nginx: [emerg] "proxy_timeout" directive is not allowed here

etc ...

I did respect the context this time.

Thx