Once I noticed an error in the /var/log/nginx/error.log:
[error] 29461#29461: *1 connect() failed (111: Connection refused) while connecting to upstream, client: 192.168.5.5, server: _, request: "GET /iredadmin/ HTTP/2.0", upstream: "uwsgi://127.0.0.1:7791", host: "192.168.5.1"
The client tried to open iredadmin, which did not open in the browser.
In the config /etc/nginx/templates/iredadmin.tmpl I found:
include uwsgi_params; uwsgi_pass 127.0.0.1:7791; uwsgi_param UWSGI_CHDIR /opt/www/iredadmin; uwsgi_param UWSGI_SCRIPT iredadmin; uwsgi_param SCRIPT_NAME /iredadmin;
Check if something works on port 7791 (should be LISTEN):
netstat -na | grep LISTEN | grep 587
It turned out that nothing was running on this port, so I determined that to solve this problem, you just need to start the iredadmin service:
sudo service iredadmin start
After that, the error disappeared and iredadmin opened in the browser.
See also my articles:
Install and configure Nginx
Installing and configuring iRedMail