The paths to ssl_certificate and ssl_certificate_key are correct but this path wasn't accessible from my current_user.
Since, I installed iRedMail from root user and NginX from my current_user therefore I made current_user chown /etc/ssl
Do I need to make any modifications to permissions of www-data web server user as well?
/etc/ssl/certs has tons of Verisign, StartCom etc. symlinks to /usr/share/ca-certificates/mozilla/xxxx-yyyy.crt files
2014/04/15 20:43:31 [emerg] 26997#0: "proxy_pass" cannot have URI part in location given by regular expression, or inside named location, or inside "if" statement, or inside "limit_except" block in /etc/nginx/sites-enabled/default:37
[Tue Apr 15 20:43:40.712133 2014] [mpm_prefork:notice] [pid 20325] AH00169: caught SIGTERM, shutting down
[Tue Apr 15 20:43:42.030066 2014] [mpm_prefork:notice] [pid 27041] AH00163: Apache/2.4.6 (Ubuntu) OpenSSL/1.0.1e mod_wsgi/3.4 Python/2.7.5+ configured -- resuming normal operations
[Tue Apr 15 20:43:42.030265 2014] [core:notice] [pid 27041] AH00094: Command line: '/usr/sbin/apache2'