We have internal users with @companyx.co.nz email addresses on the domain.
We have an external company who use @externalcompany.co.nz.
A single user on our domain (email@example.com) can't seem to receive messages from a single user on the external domain (firstname.lastname@example.org).
However, Bill (ext) can send to other users on our domain (int). And other members of the external domain/company can send to Sam (int) fine and others on our domain.
Bill (ext) receives no bounce back or errors.
SBS 2008 running Exchange 2007.
I've logged into OWA offsite as Sam to check that it's not just their Outlook software onsite filtering out the sender or some other reason but the message doesn't display in OWA either.
There is a forwarder setup from Sam to Alan (keeps copy in Sam's mailbox) and when Bill sends an email to both Sam and Alan, Sam does not receive it, Alan does.
Where would one look next?