WIN SBS 2003 SMTP traffic increased

Does anybody had before this issue and can give me a help to sort it out. Since 2 day ago my server win 2003 is eating a lot of te broadband, and after i checked where is going everything i seen that SMTP service is taking all the broadband, i have huge pings e.g. 700-800 ms and there is no mail incoming or going and of course i see some strange IP from different locations.