Mail Delivery Problem

Hello

I have and odd problem. I recently migrated from 2003 -> 2010 -> 2013. Everything seems to be working fine except one circumstance.

When sending mail from user A to user B using the Outlook client, I get the following error.

IMCEAEX-_o=First+20Organization_ou=First+20Administrative+20Group_cn=Recipients_cn=user@domain

#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##

I get this error when I send mail from any Outlook client. During this process, I have installed a machine with Windows 8.1 and Office 2013. Even with a complexly fresh install, I still see the error.

When sending mail from user A to user B using OWA, mail is delivered without error.

I can also send mail from user B to user A using an Outlook client without error.

Any advice?