Exchange 2010 Bounced Email (Error 550 5.1.1 RESOLVER.ADR.ExRecipNotFound)

I've seen the "5.5.0 5.1.1" issue crop up in every Exchange environment I've worked on. The symptom is: a user tries to send a message to a recipient that has been migrated from a previous version of Exchange and they receive an NDR with the error: IMCEAEX-_O=EXCHANGEITUP_OU=EXCHANGE+20ADMINISTRATIVE+20GROUP+20+28FYDIBOHF23SPDLT+29_CN=RECIPIENTS_CN=TEST+20USER@exchangeitup.com
#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ## .
Luckily there are a couple easy fixes that will take care of the problem.

On the client side

If there's just a few users who have this problem, you can have them empty their Outlook Auto-complete cache, which is housing the old/outdated email address.

To do this:

In Outlook, go to File > Options > Mail > scroll down to the Send Messages section and then click on the Empty Auto-Complete List button.

**Note** This will empty all Auto-complete entries so they will have to manually find contacts in the GAL, or type the email addresses to rebuild the list.

On the Exchange side

If you have tons of users with the problem, you can add an X500 address to the affected recipient's mailbox, which will allow those users to send even if they have the old/outdated address in their Auto-complete list.

To do this:

We'll need to translate the IMCEAEX error into an X500 address.

First, copy the IMCEAEX address so you get:
_O=EXCHANGEITUP_OU=EXCHANGE+20ADMINISTRATIVE+20GROUP+20+28FYDIBOHF23SPDLT+29_CN=RECIPIENTS_CN=TEST+20USER@EXCHANGEITUP.COM

In the EMC, open up the Properties on the recipient's mailbox, then go to the Email Addresses tab.

Click the Down Arrow next to the Add button, select Custom Address.

In the Email Address field, paste the IMCEAEX address and edit it, following this key:

_ is a /
+20 is a Space
+28 is a (
+29 is a )

The edited address will look like this:
/O=EXCHANGEITUP/OU=EXCHANGE ADMINISTRATIVE GROUP(FYDIBOHF23SPDLT)/CN=RECIPIENTS/CN=TEST USER

**Note** You'll need to change "/O=EXCHANGEITUP", "/OU=" and "CN=TEST USER" to reflect your environment, and be sure to remove "@DOMAIN.COM" from the end of the address as it's not needed.

In the Email Type field, type in X500.

Click OK.

You'll see the new X500 address listed in the Email Addresses list.

Now your users should be able to use Outlook Auto-complete to email the old address.