When Legacies Are Baggage (Resolving the #550 5.1.1 RESOLVER.ADR.ExRecipNotFound error during Migration)

I was working with an education customer this week when I came upon an interesting problem related to mail routing for a specific user. This user was migrated from one domain to another and mailbox-enabled for the new Exchange 2007 environment after their historical information had come over. The user had three different SMTP email addresses, but the primary SMTP address, username@guessme.edu, kept returning mail as undeliverable. The error information looks as follows.

Delivery has failed to these recipients or distribution lists:




The recipient's e-mail address was not found in the recipient's e-mail system. Microsoft Exchange will not try to redeliver this message for you. Please check the e-mail address and try resending this message, or provide the following diagnostic text to your system administrator.


Diagnostic information for administrators:

Generating server: HUBTransport.guessme.edu


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


A quick look at the recipient (using get-mailbox | FL) shows the following (I have edited down the results to the most relevant information):


Database : IT-MAILBOX01\SG01\Database01

DeliverToMailboxAndForward : False

RetentionHoldEnabled : False

EndDateForRetentionHold :

StartDateForRetentionHold :

ForwardingAddress :

ProhibitSendQuota : unlimited

ProhibitSendReceiveQuota : unlimited

RecipientLimits : unlimited

SamAccountName : username

Alias : username

DisplayName : Last, First

EmailAddresses : {smtp:First.Last@guessme.edu, smtp:username

                                       @domain.guessme.edu, SMTP:username@guessme.edu}

HiddenFromAddressListsEnabled : False

LegacyExchangeDN : /o=guessMeMail/ou=Exchange Administrativ

                                       e Group (FYDIBOHF23SPDLT)/cn=Recipients/


MaxSendSize : unlimited

MaxReceiveSize : unlimited

EmailAddressPolicyEnabled : True

PrimarySmtpAddress : username@guessme.edu

RecipientType : UserMailbox

RequireSenderAuthenticationEnabled : False


Again, mail flowed just fine to the non-primary SMTP addresses. What was particularly interesting is that when Outlook was used, the user name was fully resolved against the address book and mail bounced. When Outlook Web Access (OWA) was used, the mail didn't bounce, even though name resolution was occurring.


Take a look at the relevant attributes from the Get-Mailbox cmdlet. The problem in our case happened to be the LegacyExchangeDN. Unknown to me (and the Exchange admin I was working with), the user account was migrated from the old domain, the alias changed (by removing the trailing number 1), and the mailbox was requested. However, the LegacyExchangeDN gets created at the time of migration. What should've happened is that the AD migration team should have altered the alias first, then migrated.


The fix is pretty straight forward. Remove the 1 from the LegacyExchangeDN attribute in AD Users and Computers. Once we did this, mail began to flow again.


UPDATE: My customer pointed me to another blog that offers a great scripted solution for this. http://mostlyexchange.blogspot.com/2007/08/exchange-2007-legacyexchangedn-and-mail.html