Whe connecting thunderbird for the first time to Zarafa, there are a few differences between the two.
The most annoying is the 'Deleted Items' versus 'Trash'.
When they are not correctly mapped you end up with 2 trash folders, depending on the interface you use.
This is quite inconvenient.
1. Completely exit Thunderbird if it is running.
2. Make a temporary backup copy of your profile folder (or at least "prefs.js").
3. Open your "prefs.js" file with a text editor such as Notepad to find the server# used to represent your IMAP account. It could be "server2", "server5", "server7", or some other number depending on your own individual account setup. Look for a line similar to this, corresponding to your own IMAP acccount:
user_pref("mail.server.server2.hostname", "mail.YourImapProvider.com");
4. Insert a line like the following into "prefs.js", with the correct server# and correct name for the Trash folder:
user_pref("mail.server.server#.trash_folder_name", "");
For example:
user_pref("mail.server.server2.trash_folder_name", "Deleted Items");