From the NDR message if you find the IMCEAEX address, you CAN convert this to X500 address & ADD it as another email address to the correct mailbox or distribution group. I have wrote an small PowerShell Script to convert IMCEAEX address to X500 address quickly.

Here is the script. Copy this script and paste into notepad. Save it as Convert-X500Address.ps1. Run the script with the parameter of IMCEAEX address.

E.g., Convert-X500Address  -IMCEAEXString “IMCEAEX-_O=EXCH_OU=EXCHANGE+20ADMINISTRATIVE+20GROUP+20+28FHSDHJF23GHYED+29_CN=RECIPIENTS_CN=Don+2Doe@contoso.com”

<#
Convert-X500Address.ps1

Convert IMCEAEX string from NDR message to X500 Address format. This
Script simply displays the X500 string. Copy it and make a new
X.500 Email address to the Exchange object.

Parameter: Pass the IMCEAEX string from NDR message in double quotes

Written By: Anand, the Awesome, Venkatachalapathy

#>
param($IMCEAEXString)

((((((($IMCEAEXString.Replace(“IMCEAEX-“,””)).Replace(“_”,”/”)).Replace(“+20″,” “)).Replace(“+28”,”(“)).Replace(“+29″,”)”)).Replace(“+2E”,”.”).Replace(“+2C”,”,”)).Replace(“+5F”,”_”))

#* * * End of the Script * * *

Enjoy!