I thought I'd post this in case anyone is in a similar (desperate!!) situation.
Our company does not allow POP or IMAP on the exchange server for security reasons and I couldn't get osTicket to authenticate to the OWA server no matter what I tried...: Due to red tape I needed to come up with a solution which didn't involve changing anything on Exchange
I installed (hMail Server) and then set up a local mailbox and configured osTicket to look to this mailbox for fetching mails..
Next in Outlook I mapped the Exchange mailbox and the local mailbox as IMAP (so the messages would be copied to the mailbox rather than downloaded to a pst in Outlook if you choose POP)
Lastly I set up a rule in Outlook to copy incoming mails from the Exchange mailbox -> local mailbox and set up the scheduled task to fetch the mails
A bit long winded compared to having OsTicket talk directly to exchange I know but set this up in a fraction of the time I wasted trying to get OsTicket to talk to Exchange so it's worth the extra steps for us lol! ;)