Here are results of tail -n40 /var/log/nginx/error.log
2017/03/27 18:40:36 [error] 25441#0: *4 open() "/var/www/roundcubemail" failed (13: Permission denied), client: 216.36.162.155, server: _, request: "GET /mail HTTP/1.1", host: "mail.domain.com", referrer: "http://www.iredmail.org/forum/post55358.html"
2017/03/27 18:40:36 [error] 25441#0: *4 open() "/var/www/html/favicon.ico" failed (2: No such file or directory), client: 216.36.162.155, server: _, request: "GET /favicon.ico HTTP/1.1", host: "mail.domain.com"
2017/03/27 18:40:37 [error] 25441#0: *4 open() "/var/www/html/favicon.ico" failed (2: No such file or directory), client: 216.36.162.155, server: _, request: "GET /favicon.ico HTTP/1.1", host: "mail.domain.com"
2017/03/27 18:41:41 [error] 25441#0: *4 open() "/var/www/roundcubemail" failed (13: Permission denied), client: 216.36.162.155, server: _, request: "GET /mail HTTP/1.1", host: "mail.domain.com", referrer: "http://www.iredmail.org/forum/post55358.html"
2017/03/27 18:42:09 [error] 25834#0: *1 "/var/www/html/iredadmin/index.html" is not found (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /iredadmin/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 18:42:09 [error] 25834#0: *1 open() "/var/www/html/404.html" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /iredadmin/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 18:42:19 [error] 25834#0: *1 "/var/www/html/mail/index.html" is not found (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 18:42:19 [error] 25834#0: *1 open() "/var/www/html/404.html" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 18:53:31 [error] 25834#0: *3 open() "/var/www/roundcubemail" failed (13: Permission denied), client: 52.1.11.160, server: _, request: "GET /mail HTTP/1.1", host: "mail.domain.com"
2017/03/27 19:48:54 [error] 25834#0: *4 "/var/www/html/mail/index.html" is not found (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 19:48:54 [error] 25834#0: *4 open() "/var/www/html/404.html" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 19:48:55 [error] 25834#0: *4 "/var/www/html/mail/index.html" is not found (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 19:48:55 [error] 25834#0: *4 open() "/var/www/html/404.html" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 20:20:39 [error] 6854#0: *1 open() "/var/www/html/favicon.ico" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /favicon.ico HTTP/1.1", host: "mail.domain.com"
2017/03/27 20:20:39 [error] 6854#0: *1 open() "/var/www/html/404.html" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /favicon.ico HTTP/1.1", host: "mail.domain.com"
2017/03/27 20:20:39 [error] 6854#0: *3 open() "/var/www/html/favicon.ico" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /favicon.ico HTTP/1.1", host: "mail.domain.com"
2017/03/27 20:20:39 [error] 6854#0: *3 open() "/var/www/html/404.html" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /favicon.ico HTTP/1.1", host: "mail.domain.com"
2017/03/27 20:20:39 [error] 6854#0: *2 "/var/www/html/mail/index.html" is not found (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 20:20:39 [error] 6854#0: *2 open() "/var/www/html/404.html" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 20:20:39 [error] 6854#0: *2 open() "/var/www/html/favicon.ico" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /favicon.ico HTTP/1.1", host: "mail.domain.com"
2017/03/27 20:20:39 [error] 6854#0: *2 open() "/var/www/html/404.html" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /favicon.ico HTTP/1.1", host: "mail.domain.com"
2017/03/27 20:20:39 [error] 6854#0: *3 open() "/var/www/html/favicon.ico" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /favicon.ico HTTP/1.1", host: "mail.domain.com"
2017/03/27 20:20:39 [error] 6854#0: *3 open() "/var/www/html/404.html" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /favicon.ico HTTP/1.1", host: "mail.domain.com"
2017/03/27 20:22:52 [error] 6854#0: *5 open() "/var/www/roundcubemail" failed (13: Permission denied), client: 216.36.162.155, server: _, request: "GET /mail HTTP/1.1", host: "mail.domain.com", referrer: "http://www.iredmail.org/forum/topic1253 … found.html"
2017/03/27 20:22:53 [error] 6854#0: *5 open() "/var/www/html/favicon.ico" failed (2: No such file or directory), client: 216.36.162.155, server: _, request: "GET /favicon.ico HTTP/1.1", host: "mail.domain.com"
2017/03/27 20:22:53 [error] 6854#0: *5 open() "/var/www/html/favicon.ico" failed (2: No such file or directory), client: 216.36.162.155, server: _, request: "GET /favicon.ico HTTP/1.1", host: "mail.domain.com"
2017/03/27 20:23:08 [error] 6854#0: *7 "/var/www/html/mail/index.html" is not found (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 20:23:08 [error] 6854#0: *7 open() "/var/www/html/404.html" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 20:23:16 [error] 6854#0: *7 "/var/www/html/mail/index.html" is not found (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 20:23:16 [error] 6854#0: *7 open() "/var/www/html/404.html" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 21:44:35 [error] 6854#0: *12 "/var/www/html/mail/index.html" is not found (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 21:44:35 [error] 6854#0: *12 open() "/var/www/html/404.html" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 21:44:40 [error] 6854#0: *12 "/var/www/html/mail/index.html" is not found (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 21:44:40 [error] 6854#0: *12 open() "/var/www/html/404.html" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 21:49:01 [error] 8661#0: *1 "/var/www/html/mail/index.html" is not found (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 21:49:01 [error] 8661#0: *1 open() "/var/www/html/404.html" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 21:49:02 [error] 8661#0: *1 "/var/www/html/mail/index.html" is not found (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 21:49:02 [error] 8661#0: *1 open() "/var/www/html/404.html" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 21:49:07 [error] 8661#0: *1 "/var/www/html/mail/index.html" is not found (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"
2017/03/27 21:49:07 [error] 8661#0: *1 open() "/var/www/html/404.html" failed (2: No such file or directory), client: 216.36.162.155, server: , request: "GET /mail/ HTTP/1.1", host: "mail.domain.com"