Windows – Exchange 2010 – After removing accepted domain, emails still going to IMCEAEX instead of external MX

From your question, it sounds like you have not added the domain to the Exchange Server as an Authoritative Domain for your Exch2010 Org Config, or added an email policy.

Open the Exch 2010 EMC, expand the Organization Configuration, and select Hub Transport (oh yeah, do this on a hub server, not an edge server). Select the "accepted domains" tab, and on the right-hand panel, select "new accepted domain". Then give the domain a common name and enter the FQDN for the otherdomain.xx domain.

Next, click the tab for email address policies in the same section, and select "new email address policy". Give it a common name, hit next, then if you want the policy to apply to everyone in AD, simple leave the next screen as is. You can specify having the email policy only apply to certain AD users by setting custom attributes on users and then selecting that attribute here, if you so desire.

Hit next, hit Add by the green + sign, and then you can define how the email addresses will be generated (alias, fn/ln, fi/ln, etc), then, just to make sure you entered it right as a accepted domain, you can select the radio button for "select the accepted domain for the email address", hit browse, and see if the domain you added is there.

Hit next, then hit next to apply immediately (or set a schedule for later).

I used Powershell to disable updating email address from recipient policy:

Get-MailContact -OrganizationalUnit "domain.local/OU" | set-mailcontact -emailaddresspolicyenabled $false

Then i used ADModify.net to strip off the secondary SMTP addresses assigned to contacts. It worked like a charm.