In Exchange 2010 we have our main domain name and then we have two other domain names, so each user they have 3 possible email addresses they can use. We can receive from all three addresses internally. However we can only receive from external email addresses to the main email address. If I try to send an email address from like gmail I get the following error: 554 5.7.1 Error: deny openrelay. Where would I need to add these other email addresses in Exchange?