I got similar problems with v1.6 ST on Linux.
I sent a blank/new ticket through my email client and not through the browser but it's not getting "auto created" (never does).
But I create a ticket manually through the osTicket web page and then replies with my email client (outlook) osTicket adds it accordingly.
The NEW ticket email arrives but it's just not getting into the ticket system, running a Apache Linux server. Anyone know a solution or have similar problem?