SBS EXCHANGE 2000 E-MAIL

all of the sudden, the sbs exchange 2000 stopped going to pick up the e-mail from the 15min schedueled time. I redo the internet & exchange configuration in the administration console but still not doing it automatically. the e-mail is not coming from the host e-mail external server. We are able to see it in the WebMail server but it does not come in into exchange. Any ideas to solve it? thanks for your help