Step 1: Open a web browser and log into your server via http://yourdomainname:2096
Step 2: Click on Webmail Home on the left pane.
Step 3: Navigate to the option Account Preferences and enable the option Automatically Create Folders.
Step 4: Now, log into webmail and then navigate to Settings > Folders.
Step 5: Create and enable a folder and ask the senders to send emails to account+foldername@domain.com address.