Problem
When accessing the Advanced Settings of a group, you can assign an email address to the group and define who is allowed to send emails to that address. However, no matter which users or groups are granted permission, all users are able to send emails to the group email address. The configured restrictions do not take effect.
Root Cause
By default, the restrictions set for a group email address are not enforced unless a specific UCS configuration variable is enabled. Without this setting, Postfix allows all users to send emails to the group, ignoring the permissions configured in the group’s advanced settings.
Solution
To enforce the restrictions configured for the group email address, you need to set the following UCS configuration variable and restart Postfix:
ucr set mail/postfix/policy/listfilter='yes' && service postfix restart
This enables Postfix to respect the permissions set for the group. For further details, see the official documentation: Management of Mail Groups.