LegacyExchangeDN missing in mail user

Hi there,

we just received an emergency call, another consultant agency has misconfigured MMN & CMN, so that the migrated Notes users cannot send mails from Exchange to Notes users.. To be exact, if there are new created aliases / proxyaddresses it is possible, but if the Exchange users want so send mails to the existing Notes users, then the delivery will fail via Outlook. But via OWA it is successful. Long story short... the mail users created by the DirSync have no LegacyExchangeDN.

I have adjusted this for an existing Notes user and added a LegacyExchangeDN and delivery has been successful immediately.

So the question is, is there a possibility to add the LegacyExchangeDN in the process of the mail user creation?
Or might it be a permission issue?

Kind regards,