Currently we have multiple SMTP addresses setup (firstname.lastname@example.org, email@example.com, firstname.lastname@example.org) within our default domain (email@example.com). We are able to send mail in/ out just fine using the corresponding aliases for each secondary domain. Here's the thing, we've added a new domain and we can receive mail via the new domain (i.e. firstname.lastname@example.org) , but we want to do the same thing we do on the other secondary domains and send as well, but we keep getting these Undeliverables when sending from email@example.com: 'You do not have permission to send to this recipient'.
Is this a DNS issue? Is this a permission thing with in Exchange? I've read all about these 3rd party tools, and I know ours is currently working natively within Exchange, is there something I'm missing completely?