One variable to manage the max attachment size.

library/roles/roundcube/defaults/main.yml

@@ -137,3 +137,6 @@ roundcube_identity_smtp_name: identity_smtp
 roundcube_additional_plugins: []
 #roundcube_additional_plugins:
 #  - identity_smtp
+
+# In Megabytes. This affects both the nginx/apache and php configurations
+roundcube_max_attachments_size: 5

library/roles/roundcube/templates/nginx-virthost.conf.j2

@@ -41,6 +41,9 @@ server {
 
     index index.php;
 
+    # This determines the max size of attachments. Configure the corresponding php options accordingly
+    client_max_body_size {{ nginx_client_max_body_size }};
+
     # Add headers to serve security related headers
     # Before enabling Strict-Transport-Security headers please read into this
     # topic first.

library/roles/roundcube/vars/main.yml

@@ -1,7 +1,10 @@
 ---
 nginx_use_common_virthost: False
+nginx_client_max_body_size: '{{ roundcube_max_attachments_size * 2 }}M'
+
 phpfpm_default_user: '{{ roundcube_user }}'
 phpfpm_default_pool_name: roundcube
+phpfpm_default_memory_limit: '{{ roundcube_max_attachments_size * 4 }}M'
 redis_install: False
 http_port: 80
 https_port: 443
@@ -29,8 +32,8 @@ phpfpm_default_memory_limit: "64M"
 
 php_global_settings:
   - { option: 'zlib.output_compression', value: 'Off' }
-  - { option: 'post_max_size', value: '6M' }
-  - { option: 'upload_max_filesize', value: '5M' }
+  - { option: 'post_max_size', value: '{{ roundcube_max_attachments_size }}M' }
+  - { option: 'upload_max_filesize', value: '{{ roundcube_max_attachments_size }}M' }
   - { option: 'session.auto_start', value: 'Off' }
   - { option: 'suhosin.session.encrypt', value: 'Off' }
   - { option: 'session.gc_maxlifetime', value: '21600' }