We have two trusted Exchange forests -- domain1 and domain2. We tried to use a utility (Forefront Identity Management) to sync the AD user accounts/contacts and by accident caused duplicate email accounts/contacts in both forests. It prevented users from sending email cross the forests with the error:
"More than one user has this e-mail address. #550 5.1.4 RESOLVER.ADR.Ambiguous; ambiguous address ##"
So we got into AD to delete all the sync-ed accounts/contacts in the destination domains, and thought that should be it. Unfortunately, the issue remained except the error is different:
"The e-mail address you entered couldn't be found."
Further investigation found the recipient email address we carefully typed out in the recipient field is correct for sure as we can see but from the bounced NDR we can see after sending the recipient address being altered to an ExchangeLegacyDN such as:
And that's why got the "address not found" error.
Again, it only happens while trying to send cross the forest. There is no issue while using OWA.
And the most strange thing is, it only happens to many but NOT all users, whether it is in cached mode or not. We suspected it is cache issue so we did update OAB, GAL, redownloading OAB, etc. But the issue still remains.
Any help is appreciated.