From: DeskNow Knowledge Base
http://www.desknow.com/kb/

How do I configure Mozilla Thunderbird to connect to DeskNow via IMAP?
http://www.desknow.com/kb/idx/4/105/article/
  1. in Thunderbird, select Tools/Account settings from the menu
  2. click 'Add account...'
  3. select email account and click Next
  4. enter your name and DeskNow email address
  5. select IMAP as the server type and provide the address of your DeskNow server (name or IP address)
  6. complete the remaining steps
  7. once the account is created, open again the 'Account settings' dialog, and click on the 'Server settings' item under the new account. Review server address and port, whether to use SSL, etc.
  8. Enable  the 'Use secure authentication' option. 
  9. click on the 'Advanced...' button and uncheck the option 'Show only subscribed folders' to view all your DeskNow folders.
  10. By default Mozilla will try and store sent messages into a folder called 'Sent'. This is probably not present in DeskNow (by default it uses the Outlook conventional name, 'Sent Items'). Make sure that you open The Inbox folder once to force Thunderbird to display all the server-side folders (like 'Sent Items') and then change the settings in Account settings/Copies & Folders.
  11. Thunderbird uses 'Trash' as the name for deleted items, whereas DeskNow uses 'Deleted Items' (or your localized version if your language setting is not English). See this article in the Mozilla knowledge base to make Thunderbird use a different name for the trash folder: http://kb.mozillazine.org/IMAP_Trash_folder
  12. by default, Thunderbird stores spam messages in the local 'Junk' folder. To have it store on DeskNow, select Tools/Junk Mail Controls from Thunderbird's menu and select the 'Other' option and select the Spam folder in your DeskNow account. This step is optional.
  13. since Thunderbird and DeskNow both support the IDLE imap command, new email notification on the currently open folder is immediate. You may reduce traffic and server load by increasing the setting 'Check for new messages every x minutes'. Use a setting lower than 30 minutes (ex. 28).