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My nginx.conf:

user www-data www-data; ## Default: nobody
worker_processes 5; ## Default: 1
error_log /var/log/nginx/error.log;
pid /var/run/nginx.pid;
worker_rlimit_nofile 8192;

events {
worker_connections 4096; ## Default: 1024
}

http {
include /etc/nginx/proxy.conf;
include /etc/nginx/fastcgi.conf;
index index.html index.htm index.php;

default_type application/octet-stream;
log_format main '$remote_addr - $remote_user [$time_local] $status '
'"$request" $body_bytes_sent "$http_referer" '
'"$http_user_agent" "$http_x_forwarded_for"';
access_log /var/log/nginx/access.log main;
sendfile on;
tcp_nopush on;
server_names_hash_bucket_size 128; # this seems to be required for some vhosts


server {
listen email_port;
server_name email_server.domain.tld;
ssl on;
ssl_certificate /etc/ssl/certs/cert.org.chained.crt;
ssl_certificate_key /etc/ssl/private/priv.key;
include /etc/nginx/sslciphers.conf;
ssl_session_timeout 60m;
error_log /var/log/nginx/error-proxy_zobe.log;

location / {
proxy_pass https://ip_email_server:email_port;
}
}

}


Error message from the reverse-proxy side:


2017/01/10 11:01:40 [error] 23144#23144: *8 upstream prematurely closed connection while reading response header from upstream, client: ip_cellular, server: email_server.domain.tld, /ip_email_server:email_port/favicon.ico", host: "email_server.domain.tld:email_port", referrer: "https://email_server.domain.tld:email_port/SOGo/"

Log from the email server side:

reverse_proxy_ip - - [10/Jan/2017:10:23:44 +0100] "GET /favicon.ico HTTP/1.0" 444 0 "https://email_server.domain.tld:port_number/SOGo/" "Mozilla/5.0 (Linux; Android 6.0.1; Nexus 5 Build/MMB29T) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.85 Mobile Safari/537.36"

If I bypass the reverse proxy (changing the NAT on my router) I do have access to the management web interface of my email server.

Any ideas ?

Thx