==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release):
- Deployed with iRedMail Easy or the downloadable installer?
- Linux/BSD distribution name and version:
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):
- Web server (Apache or Nginx):
- Manage mail accounts with iRedAdmin-Pro?
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

Hello
CentOS 7 with iRedAdmin Pro, MariaDB, Nginx on new release.

Also note that iRedAdmin-Pro is using Nginx now....

User reports error on file upload/attachment in the RoundCube interface.  Following this online documentation to alter:
    https://docs.iredmail.org/change.mail.a … .size.html

Checking PHP values with this command:
php -i| egrep "upload_max_filesize|post_max_size|memory_limit"
memory_limit => 600M => 600M
post_max_size => 300M => 300M
upload_max_filesize => 300M => 300M

Went to alter Roundcube webmail step but file structure possibly different.   
States:
- on RHEL/CentOS, it's /opt/www/roundcubemail/config/config.inc.php
- on RHEL/CentOS, it's /var/www/roundcubemail/.htaccess

Currently do not have that .htaccess file but have these:
- /opt/www/roundcubemail/.htaccess
- /opt/www/roundcubemail/config/.htaccess

Actually, have more .htaccess files than that but just the ones symlinked to roundcube version 1.4.9
/opt/www/roundcubemail-1.4.9/config/.htaccess
/opt/www/roundcubemail-1.4.9/.htaccess
/opt/www/roundcubemail-1.4.9/public_html/.htaccess
/opt/www/roundcubemail-1.4.9/logs/.htaccess
/opt/www/roundcubemail-1.4.9/temp/.htaccess
/opt/www/iRedAdmin-1.0/static/.htaccess

The values to add per documentation....
php_value    memory_limit   200M
php_value    upload_max_filesize    100M
php_value    post_max_size  100M

Further attempting to determine the config used by attempting searching....
grep --include={php.ini,.htaccess} -rnw / -e 'upload_max_filesize'
/etc/php.ini:810:;upload_max_filesize = 10M;
/etc/php.ini:811:upload_max_filesize = 300M;
grep --include={php.ini,.htaccess} -rnw / -e 'post_max_size'
/etc/php.ini:677:;post_max_size = 12M;
/etc/php.ini:678:post_max_size = 300M;
grep --include={php.ini,.htaccess} -rnw / -e 'memory_limit'
/etc/php.ini:405:; memory_limit = 256M;
/etc/php.ini:406:memory_limit = 600M;

So the files edited with commented out values in place for later reference on demand. 

So:
Which file gets edited to make it work and/or should the other be eliminated to alleviate questions later?

Should the Nginx syntax be: 
    $config['max_message_size'] = '100M';

Should the documentation be updated to reflect /opt/www/roundcubemail/ vs /var/www/roundcubemail/for the RHEL/CENTOS?