I have found the answer to the question.
For those looking at changing the default folder to poll from (currently INBOX) find the file 'class.mailfetch.php' located in the includes folder.
Look for the code:
function open($box='INBOX') {
Change the INBOX to a variable, or set it straight there. For example, replace the above line of code, with the following 2 lines:
global $custom_box = 'Public Folders/IT/Helpdesk';
function open($box=$custom_box) {
or
function open($box='My Folder/OsTicket') {
Judging by the comments and variable placement, this appears to be functionality OsTicket will release with a more user friendly approach in the near future!
IMPORTANT NOTE:
As of Exchange 2007 and onwards, IMAP is unable to access public folders.