From iRedMail

Mission

Enable shared folders under iRedMail with dovecot 1.2.

Requirements

• A properly working iRedMail system;
• A properly working dovecot 1.2 instead of the default 1.1;

Notes

• This article was written with a CentOS-based system in mind. Adapt it for your system.

Step-by-step configuration

• Step 1.

Add proper namespaces to dovecot.conf:

# Namespaces
namespace private {
	subscriptions = yes
	separator = /
	prefix = 
	inbox = yes
}

namespace shared {
	subscriptions = no
	separator = /
	prefix = Shared/%%u/
	location = maildir:%%Lh/Maildir:INDEX=%Lh/Maildir/Shared/%%Lu
	list = children
	hidden = no
	inbox = no
}

The private namespace is the default namespace, if it's already in the config do not add it a second time. shared is the one we need here.