Mail does not reach mail-enabled public folders

This is a permissions issue. Exchange public folders require the "Anonymous" user to have at least Contributor rights in order to receive email from external sources (including POPcon).

Fix

1. In Outlook, right-click the public folder and choose Properties.
2. Go to the Permissions tab.
3. Click Client Permissions.
4. Select the Anonymous user and set their role to Contributor.
5. Click OK.

Screenshots — step by step