My webhost has pretty bad anti-spam, and so my ticket system gets a lot of spam. To help with it I made a plugin which uses 3 different systems (content analysis, SPF checks of the email domain, IP and email checks against known blocklists) and based on that can block spam. For scenarios where it does not block the spam, it also has a handy UI on the ticket to one click delete the ticket and put the spammers email into the OS Ticket block list.
Totally free and open source https://github.com/rmaclean/osticket-spamblock
