How to remove non-routable domains from your Exchange Organization
I wrote a small Tutorial explaining the process to remove non-routable domains from an Exchange Server 2013 organization.
Some organizations have non-routable domains wandering in the SMTP address of Exchange/Mailboxes. It is nice to keep the environment clean and remove non-used configuration, also if you are planning to have a hybrid environment, it is interesting to remove those invalid domains to some road-blocks down the road when integrating with Office365.
REad more at source: http://itprocentral.com/how-to-remove-non-routable-domains-from-your-exchange-organization/