We have a split SMTP domain. Email from the outside world is delivered to a central mail platform at our Geneva office. Mail is the routed to the correct mail server. A freshly built 2013 server has been deployed for a group of users. The 'Accepted Domain' has been configured as an 'Internal Relay' domain and we have a dedicated 'Send Connector' set up to route unknown email addresses to Geneva; this has been working during testing for internal>external tests and internal>internal (relay to other mail server) tests. However when we came to open up SMTP Geneva>Ex2013 for mail delivery emails are getting bounced back to the sender with the following NDR:
Delivery has failed to these recipients or groups:
<user@domain.com>
The email address you entered couldn't be found. Please check the recipient's email address and try to resend the message. If the problem continues, please contact your helpdesk.
The following organization rejected your message: <London Mail Server>.
Diagnostic information for administrators:
Generating server: <Geneva Mail Server>
<user@domain.com>
<London Mail Server>
Remote Server returned '<<London Mail Server> #5.1.1 smtp; 550 5.7.1 Unable to relay>'
I have verified the users exist and mailboxes are online, sending email out works, but a reply fails. I have bypassed the Geneva server and performed a manual telnet into Ex2013 from outside the network and I was successfully able to send a test email to a Ex2013 mailbox from an external email address that would have failed using a normal email.
Any assistance in understanding why Ex2013 would not be accepting the mail from Geneva and just delivering it to the mailbox would be appreciated and it sounds like it's perhaps trying to relay that email back to Geneva and failing.
Thanks,
PT