my company is using windows server 2003 + exchange 2003 .. we have 3 domains with 1 fixed IP in the server ...but this 3 domain DNS hosting in 3 different dns hosting company . we are facing a problem that 1 of the domain cannot receive email from some domains. for sure, it can receive emails normally some many domain. i have tried to change DNS hosting company but still having same problem. also this 3 domain also secure by the same spam and anti-virus application in the server. pls help .. many many thank you!