Unable to Relay. NDR generated for active account

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

February 23rd, 2015 12:14pm

Hi,

Some troubleshooting steps:

1. Restart the transport services on both London and Geneva Mail Server.

2. Temporarily disable the firewall and AV programs on both servers.

3. Check if there are any DNS issues when resolving the target transport server in message tracking log.

Thanks,

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February 24th, 2015 7:55am

Hi Simon,

I've done those things and nothing has made any difference. In completing my own testing I added a new Send Connector to an external Exchange 2013 server to route emails direct to the London office via a Smart Host rather than an MX lookup - this meant I could bypass the Geneva head off to test. Sending an email direct to London's Ex2013 via this Send Connector the email was delivered to the mailbox. But disabling this Send Connector and have the email route via MX through the Geneva office, the email hit the London Exchange server (thats where the NDR was generated) and bounce back as "The email address you entered couldn't be found" "#5.1.1 smtp; 550 5.7.1 Unable to relay>'" - I know the mailbox is there an OK as I send a email into in not 5 minutes before using the custom Send Connector as above. There is something on Ex2013 that when it receives the email communication via the Geneva office the email address cannot be recognised. The NDR does contain the correct valid email address of the user.

Thanks,


PT

February 24th, 2015 9:13am

Issue was not actually to do with Exchange but rather the Geneva mail system. 
  • Marked as answer by PTechS 2 hours 4 minutes ago
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February 25th, 2015 4:50am

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