[otrs] How do I get tickets submitted via web interface to use custom postmast filters

I have created a custom filter which works when receiving mail via pop3. When I submit a ticket through the web interface though... it doesn't use this filter. Is there a setting or something else which I can modify to get ALL tickets to use these custom filters? Also... how do you respond within the same thread. It seems like whenever I respond, it starts a new thread.