EDIT: TL;DR, wasn't server side, was client issue.

Looks like this is the result of bad autocomplete entry. I wasn't aware that the functionality the nk file provided is now integrated with the mailbox in 2013. I was fairly confident we entered the recipient from the GAL directly and didn't autocomplete the entry which led me away from this as a possibility. Either way, deleting the cached address appears to have resolved the issue. I'm going home now. =P

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Apologies in advance if in the wrong forum. Looking for assistance in troubleshooting NDR for an external contact. Full disclosure, not an exchange admin, but have some limited access to troubleshoot the service.

We are a k-12 institution with a distro that emails a number of district superintendents. The members of this distro are all external contacts. Recently, these contacts were deleted accidentally and recreated. After this process, we're seeing a strange symptom:

Internal sender internal@company.org sends to contact with primary SMTP address external@district.k12.ca.us

Mail is delivered to external@district.k12.ca.us mailbox, but the internal user immediately gets an NDR for external@company.org which it would since it's an external contact and has no internal mailbox.

This has caused a lot of confusion with internal senders thinking their emails are not getting to the recipient, even though they are. If I check out the contact, there are no secondary email addresses and the primary is correct. So, where is the internal address being generated from and how can I begin troubleshooting how to stop the mistaken "internal delivery" NDR?

Diagnostic information for administrators:

Generating server: cas.company.org

IMCEAEX-_O=COMPANY_OU=EXCHANGE+20ADMINISTRATIVE+20GROUP+20+28FYDIBOHF23SPDLT+29_CN=RECIPIENTS_CN=external@company.org
#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##

Original message headers:

Received: from mailboxdb.company.org ([fe80::d08:2ada:ed04:7822]) by cas.company.org
 ([::1]) with mapi id 14.03.0235.001; Mon, 31 Aug 2015 16:20:52 -0700
Content-Type: application/ms-tnef; name="winmail.dat"
Content-Transfer-Encoding: binary
From: Internal User <internal@company.org>
To: External Contact
        <IMCEAEX-_O=COMPANY_OU=EXCHANGE+20ADMINISTRATIVE+20GROUP+20+28FYDIBOHF23SPDLT+29_CN=RECIPIENTS_CN=external@company.org>,

• Edited by FCOE_Tech 10 hours 38 minutes ago solution

Does the mail contact has 2 SMTP addresses