Don't waste time considering this
option.
Seriously.
I've had the same problem this summer, and I have tried
to implement Openchange protocol.
I have succeeded in connecting to mailboxes and in
downloading messages on a local mailbox.
I've also piped the mails collected through Postmaster
script onto OTRS.
I did a LOT of work but the issues remains simply too
much to use this solution in a production
environment.
So definitely go and ask to enable POP3 or IMAP on
per-mailbox basis: this is the only reliable way,
now.
If you really need it, your
mail admins should (and could) do
this.
Period.
Ciao, d.