I have not used OSTicket; I also note that this issue is several days old, so it's probably resolved by now...but:
Didja check the server logs? There are some security issues involved in sending mail to a pipe, and it could be that either the server doesn't have permission to do so, or the permissions on the file or pipe are such that the server simply won't write to it --- I'd think it would be rather server specific ... maybe you could learn something there.
HTH,