Exchange Error: 550 5.1.1 RESOLVER.ADR.ExRecipNotFound

Sometimes you have a reason to restore a mailbox from back-up, because it was deleted by mistake or a former employee is hired again. But after restoring the mailbox, several (internal) users are not able to send email to the restored mailbox and receive an error message like: Delivery has failed to these recipients or groups. With the error code IMCEAEX #550 5.1.1 RESOLVER.ADR.ExRecipNotFound ##
In other Exchange versions the message also contains Recipient not found by Exchange Legacy encapsulated email address lookup.
(This message could also show up after migrating the mailbox to another forrest)

Exchange diagnostics

Exchange diagnostics

The first thing you probably think of to resolve the issue, is to delete the cached email address from Outlook, but that did not resolve the error message.


We just created a new account, with an old, restored mailbox, maybe we need to restart the MS Exchange Active Directory Topology service (or even the Exchange server). In this case, that did not work either.


So what is the solution to this problem!? I was pointed at this blog (credits to the writer of that blog!). It was the same error code we received, but not the exact same message (Recipient not found by Exchange Legacy encapsulated email address lookup is missing from our message) but that makes no difference. It pointed me in the right direction, the LegacyExchangeDN was changed since we created a new account/ restored the mailbox and was not associated with the new account.

Attribute editor

Exchange internally still uses an X.500 addressing schema. So when an user sends an email internally to the restored mailbox, the old X.500 address is used and therefor Exchange is not able to deliver the email. The user who send the email receives a Non Delivery Report (NDR) with the old ID in the form of a IMCEAEX address.

Exchange error code

We are able to rebuild the required X.500 address based on the received IMCEAEX in the NDR by using a PowerShell script.
Copy below PowerShell scipt:

$Direction = Read-Host “Ingrese IMCEAEX”
$Remplazo= @(@("_","/"), @("\+20"," "), @("\+28","("), @("\+29",")"), @("\+2C",","), @("\+3F","?"), @("\+5F", "_" ), @("\+40", "@" ), @("\+2E", "." ))
$Remplazo | ForEach { $Direccion = $Direccion -replace $_[0], $_[1] }
$Direccion = “X500:$Direccion” -replace “IMCEAEX-“,”” -replace “@.*$”, “”
Write-Host $Direction

Open PowerShell ISE and past the script.

Powershell code

Click on the Play button to run the script and it will now ask you to enter the IMCEAEX, which you received in the NDR. It starts with IMCEAEX and ends with the domainname. 

Powershell code

Paste it in the PowerShell window and press ENTER. You now receive the X.500 address.

The last step is to enter the received X.500 address to the restored mailbox. You can do that by opening the user account from ADUC, on the Attribute Editor tab go to proxyaddress.

Attribute editor

Click on Edit and paste the X.500 address in the Value to add box, click on Add and OK (twice)

Multi-valued String editor

It is also possible to add the X.500 address to the mailbox by using the Exchange; In Exchange 2010 you can use the Exchange Management Console. In Exchange 2013 and 2016 you can use ECP.
On the e-mail addresses tab you enter the X.500 address (below is a print screen from Exchange 2010)

Exchange user properties

Your subtitle here

After adding the X.500 address, we are now able to send internal e-mail to the restored mailbox!


  1. There are some minor syntax issues with the script. Try this one instead:

    $Direction = Read-Host “ENTER IMCEAEX”
    $Replacement= @(@(“_”,”/”), @(“\+20”,” ”), @(“\+28”,”(“), @(“\+29”,”)”), @(“\+2C”,”,”), @(“\+3F”,”?”), @(“\+5F”, “_” ), @(“\+40”, “@” ), @(“\+2E”, “.” ))
    $Replacement | ForEach { $Direction = $Direction -replace $_[0], $_[1] }
    $Direction = “X500:$Direction” -replace “IMCEAEX-“,”” -replace “@.*$”, “”
    Write-Host $Direction

  2. Thanks Dean! I see WordPress screws up the script 🙁
    I need to figure out how to change this on the blog, but will change it.

  3. I didn’t noticed script correction in comments. 🙂 So I had to figure it out myself. You saved my behind, too!

Leave a Reply

Your email address will not be published.