I'm running 2003 SBE server with Exchange 2003. I'm getting the following error. 553 Sorry, that domain isn't in my list of allowed rcpthosts. Your site here says to look at smart host....What is smart host and is t his the fix for it? We have 2 domains one is steelsystemsplus.com and metalrooftech.com. The steelsytemsplsu.com emails fine but the other doesn't email to ONE email address. When we send it from the steelsystemsplus account the email goes thru. HELP! I'm new at this IT stuff and am getting bet one to fix this problem.