Here we are going to discuss one of the common issue which we face in our day to day life, I’m sure all the Exchange Admin would have faced this at least once in their experience. For some reason if we disable the mailbox and recreate a new mailbox with an existing AD account users may get NDR when they are sending email by choosing from local cache.

In this scenario I have user called John, for some reason I disabled the mailbox and recreated a new mailbox with an existing AD account. When others
trying to send an email by choosing from local cache they will receive below NDR.

Why am I getting this NDR?

That is because local cache deliver the emails with the help of LegacyExchanceDNvalue which would be identical for each mailbox.

Disabled mailbox DN: (which is stored in cache)

/o=First Organization/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=John568

Newly created mailbox DN:

/o=First Organization/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=Johnd01

In this scenario you can find the difference at the end of LegacyDN value which is non-identical.

How to fix this? I can ask my users to delete the local cache or choose from GAL. But is it possible to educate/communicate all the users if I have more than 10k in my organization. I don’t think it’s possible.

Better way to fix this from the server end by changing the new mailbox LegacyDN value to old mailbox LegacyDN.

How to find legacyDN value for disabled mailbox:

EMCàRecipient Configurationà Disconnected Mailboxà here you can see the LegacyDN value

How to find LegacyDN value for newly created mailbox:

StartàRunàadsiedit.mscàADSIàConnect toàDomain Naming ContextàNavigate to users locationà Properties of the accountàhere you can see the legacyExchangeDN value.

/o=First Organization/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=Johnd01

Now edit the legacyExchangeDN from “/o=First Organization/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=Johnd01to/o=First Organization/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=John568“.

That’s it now users will be able to send mails successfully by choosing from local cache.

I hope you would have enjoyed. Thanks!!!