OK I had this problem when my setup was the following.
Exhcnage mailbox with IMAP Protocol enabled.
when OSticket import (fetch) those emails they appear as tickets, when I delete them they reappear after few mintues, the reason why was I didn't select option the delete messeages after doing the fetch from mailbox. therefore all old tickets gets recreated afterwords.
I'm not sure if you have similar setup!
I hope this info will help