IMCEAEX NDRs and how to fix them…

Matt Ellis
Oct 19, 2018 · 3 min read
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If you’ve ever migrated email, restored email or aimlessly messed around with mailboxes and email address attributes, chances are that you’ve encountered non-delivery reports (NDR) with an IMCEAEX error similar to this:

IMCEAEX-_O=ORGNAME_OU=EXCHANGE+20ADMINISTRATIVE+20GROUP+20+28FYDIBOHF23SPDLT+29_CN=RECIPIENTS_CN=fcbdf1571cd0480839997fe4f620b70@domain.com

The reason this happens is that in Exchange Server, internal emails are addressed and routed using X.500 addresses, rather than with SMTP addresses. This X.500 address is found within Active Directory as the legacyExchangeDN attribute. When that legacyExchangeDN/X.500 address can no longer be resolved to a recipient, a 5.1.1 NDR occurs.

In my experience this happens most frequently when migrating email from one Exchange org to another. Post-migration people go to reply to one of their old/migrated emails and they end up with this NDR in their mailbox.

So, how do you fix this? Well, you have one of two methods available to you:

Get the legacyExchangeDNs from the source domain

To do this you can use a command similar to the following:

Set-Mailbox -Identity "first.last@destdomain.com" -EmailAddresses @{add="X500:/O=ORGNAME/OU=EXCHANGE ADMINISTRATIVE GROUP (FYDIBOHF23SPDLT)/CN=RECIPIENTS/CN=fcbdf1571cd0480839997fe4f620b70"}

Use the NDR to create an X.500 address

  • Replace any underscore character (_) with a forward slash character (/)
  • Replace “+20” with a space
  • Replace “+2E” with a full stop (period, for you yanks)
  • Replace “+28” with an opening bracket character (
  • Replace “+29” with a closing bracket character )
  • Delete the “IMCEAEX-” string from the beginning
  • Delete the “@domain.com” string at the end
  • Add “X500:” to the beginning

So:

IMCEAEX-_O=ORGNAME_OU=EXCHANGE+20ADMINISTRATIVE+20GROUP+20+28FYDIBOHF23SPDLT+29_CN=RECIPIENTS_CN=fcbdf1571cd0480839997fe4f620b70@domain.com

Will become:

X500:/O=ORGNAME/OU=EXCHANGE ADMINISTRATIVE GROUP (FYDIBOHF23SPDLT)/CN=RECIPIENTS/CN=fcbdf1571cd0480839997fe4f620b70

Now you can use the string to add your X.500 address using the following PowerShell command:

Set-Mailbox -Identity "first.last@destdomain.com" -EmailAddresses @{add="X500:/O=ORGNAME/OU=EXCHANGE ADMINISTRATIVE GROUP (FYDIBOHF23SPDLT)/CN=RECIPIENTS/CN=fcbdf1571cd0480839997fe4f620b70"}

Convert IMCEAEX to X.500 Script

You can run the script with or without the IMCEAEX string as a parameter. If you don’t supply it, you will be asked to paste it in.

ConvertIMCEAEXToX500.ps1 [-IMCEAEX]

With Parameter

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Without Parameter

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