Exchange Server 2019 Image

When you send an email to a recipient, you get IMCEAEX NDR that said “Remote Server returned ‘550 5.1.11 RESOLVER.ADR.ExRecipNotFound; Recipient not found by Exchange Legacy encapsulated email address lookup'”. This issue is happening when you migrate a mailbox with no direct path.

NDR Email


You need to create an X500 email address alias and set it to an email alias. To get X500 email address, you need to go to Active Directory Users and Computer. Make sure the “Advance Feature” view is checked.

Active Directory User and Computer - Advance Feature
Advance Feature

Then go to the user you want to add X500 email alias and go to “Attribute Editor” Tab. Find the “LegacyExchangeDN” value.

AD User Attribute Editor
Attribute Editor
$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

After you get the LegacyExchangeDN Value, you can regenerate X500 address using PowerShell Script below:

After you have X500 address, you can add it as an email alias. There some ways to do this and the easiest way is using Exchange Admin Center. Find the recipient mailbox and add an email alias to the mailbox:

Exchange Admin Center
Exchange Admin Center
Add Email Alias
Add Email Alias

Then, on the email address type field, enter “X500” and the X500 Address you get from the PowerShell Above.

X500 Email alias

Then click ok and save the changes.

That should fix the issue of sending the email to the legacy mailbox. We hope this article can help you to fix “Recipient not found by Exchange Legacy encapsulated email address lookup”. If you liked this article, then please share it with the others. You can also find us on Twitter and Facebook.


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