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Troubleshooting 5.1.1 NDRs

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Jason Crawford
I am a battle-hardened IT professional with a focus on Windows Server, Active Directory, Exchange, Office 365, and PowerShell.
How to effectively resolve the number one email related issue received by helpdesks.

The Problem

A user states they received a 5.1.1 NDR after attempting to send an email to an internal user.  The body of the NDR indicates the recipient email address is similar to this:


The reason this occurs is because the user attempted to use Outlook AutoComplete to send an email to an object (mailbox, DG, contact, etc) that has been recreated.  

The Fix

Convert the email address shown in the NDR to an x500 address we can add to the recipient's proxyAddresses.  

1. Using the conversion rules below, convert the NDR email address:

  • Replace any underscore character (_) with a slash character (/).
  • Replace "+20" with a blank space.
  • Replace "+28" with an opening parenthesis character.
  • Replace "+29" with a closing parenthesis character.
  • Delete the "IMCEAEX-" string.
  • Delete the "@mgd.domain.com" string.
  • Add "X500:" at the beginning.

2. Add the resulting address as an alias to the original recipient's mailbox using the following command in Exchange Management Shell:

Set-Mailbox "user@domain.com" -EmailAddresses @{add='convertedaddress@domain.com'}

Alternately you can use the following script to convert the NDR address:

[string]$a = Read-Host "Enter the email address listed in the 5.1.1 NDR"
$b = $a -replace 'IMCEAEX-', 'x500:'
$c = $b.Split("@")[0]
$d = $c -replace "_", "/"
$e = $d -replace "\+20", " "
$f = $e -replace "\+28", "("
$g = $f -replace "\+29", ")"
$h = $g.ToLower()

Write-Host "The converted legacyExchangeDN is:`n`n$h" -ForegroundColor Green

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