Excahnge 2016 - Crossforest migration - NDR error old messages - LegacyDN

Rcze 1 Reputation point
2021-01-13T23:22:24.607+00:00

Hi everyone, I'm helping a company that is splitting in two

Company ABC: domain ABC - Exchange 2016

New Company XYZ: Domain XYZ (different Forest) - exchange 2016

I'll migrate 65 users from ABC to XYZ.

Migration process:

1-ADMT to copy the user and password

2-Make the copied user a mail-enabled user.

3-Run the script to prepare the mailbox move

4-Move the mailbox.

As expected the mailbox in the new company(XYZ) has a x500: pointing to the legacyDN from the source side. But when a migrated user(XYZ) try to reply to an old message from user(ABC) it gets the NDR message

Diagnostic information for administrators:

Generating server: SERVER.XYZ.local

IMCEAEX-_o=The+20ABC+20Group_ou=Exchange+20Administrative+20Group+20+28FYDIBOHF23SPDLT+29_cn=Recipients_cn=UserFirstNAME+20UserLastNameb65@xyz .local Remote Server returned '550 5.1.11 RESOLVER.ADR.ExRecipNotFound; Recipient not found by Exchange Legacy encapsulated email address lookup'

I've read tons of docs and forums but I can't seem to find the solution for this, is there anything else I should be looking at besides the legacyDN?

Thank you!

Exchange Server Management
Exchange Server Management
Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
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  1. KyleXu-MSFT 26,206 Reputation points
    2021-01-14T06:22:01.573+00:00

    @Rcze

    This is an expected behavior. Here are two ways which may be useful to you:

    Way 1: Create GAL sync between two forests, then add X500 addresses for those mailboxes, in this way, email could find X500 address. But, in this way, users in two forests will could see each other.

    Way 2: Tell all users to delete the email address and enter it manually when replying to the email.

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