I had a customer who has a SBS 2003 server. It died. No worries.
They moved their email to my hosted exchange service, based on Exchange 2013. No problem.
Imported their old pst files, No problem.
However, when replying to old emails, which have the same SMTP address, it's pulling the X.500/EX address. So they get an error, cannot resolve /o=Organisation/ou=Administrative Group/cn= Recipients/cn=Username or something to that effect.
I've tried adding this as a x500 addres and EX address in their exchange email address on our hosted solution. It's still not working. Is there any way to get around this issue?
We have removed their NK2 files for auto completing email addresses. I really want to get it working on our server to be able to accept these emails. But if it's going to be too much trouble (asdi edits), then we won't do it.
This describes the problem better: https://www.simple-talk.com/sysadmin/exchange/exchange-e-mail-addresses-and-the-outlook-address-cache/